formatting: using black to check for formatting

tests/hghave.py

@@ -980,12 +980,9 b' def has_emacs():'
     return matchoutput('emacs --version', b'GNU Emacs 2(4.4|4.5|5|6|7|8|9)')
 
 
-# @check('black', 'the black formatter for python')
-@check('grey', 'grey, the fork of the black formatter for python')
+@check('black', 'the black formatter for python')
 def has_black():
     # use that to actual black as soon as possible
-    # blackcmd = 'black --version'
-    blackcmd = 'python3 $RUNTESTDIR/../contrib/grey.py --version'
-    # version_regex = b'black, version \d'
-    version_regex = b'grey.py, version \d'
+    blackcmd = 'black --version'
+    version_regex = b'black, version \d'
     return matchoutput(blackcmd, version_regex)

tests/test-check-format.t

@@ -1,7 +1,5 b''
-#require grey
-
-(this should use the actual black as soon as possible)
+#require black
 
   $ cd $RUNTESTDIR/..
-  $ python3 contrib/grey.py --config=black.toml --check --diff `hg files 'set:**.py - hgext/fsmonitor/pywatchman/** - mercurial/thirdparty/** - "contrib/python-zstandard/**" - contrib/grey.py'`
+  $ black --config=black.toml --check --diff `hg files 'set:**.py - hgext/fsmonitor/pywatchman/** - mercurial/thirdparty/** - "contrib/python-zstandard/**" - contrib/grey.py'`