DHCP still assigning an IP after setting a static address on the Raspberry Pi

I just picked up a new raspberry pi 3 and ran into a weird problem: after I assigned a static IP to eth0, eth0 was assigned both the static IP, and an IP from dhcp. I don't use debian (the distro that raspbian is based off) often, so this might be a trivial problem for folks that do. I wanted to set a static IP on eth0. Easy enough. I just cracked open /etc/network/interfaces and changed the contents from this:

# interfaces(5) file used by ifup(8) and ifdown(8)

# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'

# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

auto lo  
iface lo inet loopback

iface eth0 inet manual

allow-hotplug wlan0  
iface wlan0 inet manual  
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

allow-hotplug wlan1  
iface wlan1 inet manual  
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

to this:

# interfaces(5) file used by ifup(8) and ifdown(8)

# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'

# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

auto lo  
iface lo inet loopback

auto eth0  
iface eth0 inet static  
    address 192.168.3.3
    netmask 255.255.255.0
    gateway 192.168.3.1

allow-hotplug wlan0  
iface wlan0 inet manual  
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

allow-hotplug wlan1  
iface wlan1 inet manual  
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

Notice the changes to eth0 that assign it a static IP. This did work, but it's still getting a IP with dhcp and assigning both IPs to eth0.

This can be seen by running the command:
ip addr show eth0

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000  
    link/ether b8:27:eb:e4:19:4c brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.3/24 brd 192.168.3.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet 192.168.3.12/24 brd 192.168.3.255 scope global secondary eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::ba27:ebff:fee4:194c/64 scope link 
       valid_lft forever preferred_lft forever

That's odd. Some googleing around yielded this post on StackOverflow:
http://raspberrypi.stackexchange.com/questions/32516/multiple-ip-addresses-being-assigned

So it looks like at some point in the recent past, static IP configuration was changed from /etc/network/interfaces to /etc/dhcpcd.conf. I should have probably noticed that the interfaces file states at the top:
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'

So let's change the right file. I reverted the changes in /etc/network/interfaces back to the original and updated /etc/dhcpd.conf to the following (the last 4 lines are the important part, but I'm including the entire file for completeness):

# A sample configuration for dhcpcd.
# See dhcpcd.conf(5) for details.

# Allow users of this group to interact with dhcpcd via the control socket.
#controlgroup wheel

# Inform the DHCP server of our hostname for DDNS.
hostname

# Use the hardware address of the interface for the Client ID.
clientid  
# or
# Use the same DUID + IAID as set in DHCPv6 for DHCPv4 ClientID as per RFC4361.
#duid

# Persist interface configuration when dhcpcd exits.
persistent

# Rapid commit support.
# Safe to enable by default because it requires the equivalent option set
# on the server to actually work.
option rapid_commit

# A list of options to request from the DHCP server.
option domain_name_servers, domain_name, domain_search, host_name  
option classless_static_routes  
# Most distributions have NTP support.
option ntp_servers  
# Respect the network MTU.
# Some interface drivers reset when changing the MTU so disabled by default.
#option interface_mtu

# A ServerID is required by RFC2131.
require dhcp_server_identifier

# Generate Stable Private IPv6 Addresses instead of hardware based ones
slaac private

# A hook script is provided to lookup the hostname if not set by the DHCP
# server, but it should not be run by default.
nohook lookup-hostname

interface eth0  
    static ip_address=192.168.3.3/24
    static routers=192.168.3.1
    static domain_name_servers=192.168.3.1

And rebooted. Ta-da:

ip addr show eth0  
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000  
    link/ether b8:27:eb:e4:19:4c brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.3/24 brd 192.168.3.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::3ac0:7800:5e38:f1db/64 scope link 
       valid_lft forever preferred_lft forever