i965: Drop the missing symbols link test.

i965: Drop the missing symbols link test.

This was horribly broken and has cost everyone more time than we were
ever going to save using it.  It might have been fixable, but the
problem it was originally trying to solve can be better solved with
-Werror=missing-prototypes and -Werror=implicit-function-declaration.

Also, it was always producing a big scary warning about how the link
test was non-portable.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44928