Clean up requirements

* dict.sorted and funcsigs are not used anywhere anymore
* urlgrabber is used only in the yum based gather.py module, and thus
  only needed on Python 2
* py3 doesn't need to reinstall mock as that is part of stdlib now

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>
(cherry picked from commit c96b5358ba)

requirements.txt

@@ -1,9 +1,7 @@
 # Some packages must be installed via dnf/yum first, see doc/contributing.rst
-dict.sorted
 dogpile.cache
 flufl.lock ; python_version >= '3.0'
 flufl.lock < 3.0 ; python_version <= '2.7'
-funcsigs
 jsonschema
 kobo
 koji
@@ -14,4 +12,4 @@ ordered_set
 productmd
 pykickstart
 python-multilib
-urlgrabber
+urlgrabber ; python_version < '3.0'

tox.ini

@@ -50,7 +50,7 @@ allowlist_externals =
     sh
 commands =
     sh -c 'find . -name "__pycache__" -exec rm -rf \{\} +'
-    pip install --force-reinstall pytest mock
+    pip install --force-reinstall pytest
     pytest {posargs}
 
 [flake8]