SubmittingPatches: drop ref to "What's in git.git"

"What's in git.git" was last seen in 2010:
  https://lore.kernel.org/git/?q=%22what%27s+in+git.git%22
  https://lore.kernel.org/git/[email protected]/

Signed-off-by: Josh Soref <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jsoref

Documentation/SubmittingPatches

@@ -570,7 +570,7 @@ their trees themselves.
   master).
 
 * Read the Git mailing list, the maintainer regularly posts messages
-  entitled "What's cooking in git.git" and "What's in git.git" giving
+  entitled "What's cooking in git.git" giving
   the status of various proposed changes.
 
 == GitHub CI[[GHCI]]