Merge branch 'jc/cocci-xstrdup-or-null-fix' into maint

Get rid of a bogus and over-eager coccinelle rule.
source: <xmqq1qxd6e4x.fsf@gitster.g>

* jc/cocci-xstrdup-or-null-fix:
  cocci: drop bogus xstrdup_or_null() rule

contrib/coccinelle/xstrdup_or_null.cocci

@@ -1,11 +1,3 @@
-@@
-expression E;
-expression V;
-@@
-- if (E)
--    V = xstrdup(E);
-+ V = xstrdup_or_null(E);
-
 @@
 expression E;
 @@