Use jsonschema[format] instead of jsonschema

`jsonschema[format]` includes all the formatting dependencies of
jsonschema, meaning that we don't have to specify `rfc3339-validator`
and `rfc3987` ourselves in the requirements.in file. This also has the
benefit of meaning that if the underlying formatting packages of
jsonschema change, we will be covered and won't accidentally miss the
fact that we need to change a package.

requirements.in

@@ -13,14 +13,12 @@ click-datetime==0.2
 git+https://github.com/benoitc/gunicorn.git@1299ea9e967a61ae2edebe191082fd169b864c64#egg=gunicorn[eventlet]==20.1.0
 iso8601==1.0.2
 itsdangerous==2.1.2
-jsonschema==4.4.0
+jsonschema[format]==4.4.0
 marshmallow-sqlalchemy==0.23.1 # pyup: <0.24.0 # marshmallow v3 throws errors
 marshmallow==2.21.0 # pyup: <3 # v3 throws errors
 psycopg2-binary==2.9.3
 PyJWT==2.3.0
 SQLAlchemy==1.4.35
-rfc3339-validator==0.1.4
-rfc3987==1.3.8
 cachetools==5.0.0
 beautifulsoup4==4.10.0
 lxml==4.8.0