Bug 1260605 - Remove hack from bug 967556. r=nalexander

The hack was supposed to avoid clobbers when landing bug 967556, which
might have worked somehow back then, but doesn't do anything useful
anymore. In fact, it now breaks the display of some results in
old-configure.

build/autoconf/hotfixes.m4

@@ -16,7 +16,6 @@ dnl declares it, while the test itself is just expecting the function not to be
 dnl declared at all, and declares it differently (which doesn't matter for the
 dnl test itself).
 dnl More recent versions of autoconf are essentially doing this.
-define([ac_cv_func_], [ac_cv_func2_])dnl
 define([_AC_CHECK_FUNC],defn([AC_CHECK_FUNC]))dnl
 define([AC_CHECK_FUNC], [dnl
 patsubst(_AC_CHECK_FUNC($@), [#include.*$], [#define $1 innocuous_$1