check-code: stop forbidding return code result

There is no explication of what is the intend of that check and what is the
alternative.

I suspect this comes from the transition to the "unified test" format circa
2010. With the non zero return explicitly listed in the output explicit $?
checking became Redundant. However there is valid use case for checking $? so I
am dropping this check.

Differential Revision: https://phab.mercurial-scm.org/D10994

contrib/check-code.py

@@ -215,7 +215,6 b' utestpats = ['
             "use regex test output patterns instead of sed",
         ),
         (uprefix + r'(true|exit 0)', "explicit zero exit unnecessary"),
-        (uprefix + r'.*(?<!\[)\$\?', "explicit exit code checks unnecessary"),
         (
             uprefix + r'.*\|\| echo.*(fail|error)',
             "explicit exit code checks unnecessary",