help/config: back out 5f2a1ebd6e78

This breaks building manpages, and by association breaks building
debs. timeless has a fix coming, but it turns out we'll need to back
out 5f2a1ebd6e78 anyway, so just back it out now to fix building
packages.

mercurial/help/config.txt

@@ -1037,7 +1037,7 b' Supported arguments:'
   This tool can merge symlinks. (default: False)
 
 ``check``
-  A list of merge success-checking options::
+  A list of merge success-checking options:
 
   ``changed``
     Ask whether merge was successful when the merged file shows no changes.