Route does not get removed when it's not defined anymore

[Richard Schwab]

After changing a machines public IPv4 address and running netplan apply I noticed that the old default route was not removed.
The new route was added so I now have 2 default routes using different source IPs:

default via $gwV4 dev eth0 proto static src $oldPublicV4
default via $gwV4 dev eth0 proto static src $newPublicV4

config.yaml:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
        - $privateV4/32
        - $newPublicV4/32
      nameservers:
        addresses:
          - $gwV4
      routes:
        - to: $gwV4/32
          scope: link
          from: $privateV4
        - to: $internalNet/16
          via: $gwV4
          from: $privateV4
        - to: 0.0.0.0/0
          via: $gwV4
          from: $newPublicV4

This is tested on debian buster using netplan.io 0.95-2.