On removing a tag to a resource (port/subnet/subnetpool/network),
if the resource doesn't have the tag, skip the neutron API call to
remove_tag because the tags will be unchanged.
This will avoid one or two Neutron API calls and optimize the
performance a bit.
Partial-Bug: #1809306
Change-Id: Iffa5fbf27c64f1aad0a9bb97da9c4e7c5015a196