Remove tag validators in fits schema

[braingram]

The fits schema contains a tag validator:

asdf-astropy/asdf_astropy/resources/schemas/fits/fits-1.1.0.yaml

Line 77 in fa5f1f4

- tag: "tag:astropy.org:astropy/fits/fits-1.1.0"

for the same tag in the manifest:

asdf-astropy/asdf_astropy/resources/manifests/astropy-1.2.0.yaml

Line 16 in fa5f1f4

- tag_uri: tag:astropy.org:astropy/fits/fits-1.1.0

Look to see if this does anything and if not remove it and any other redundant tag keywords in schemas.