Revert "util: Add NONNULL macro"

We agreed in [1] not to use it since it has little value,
but making a code less readable.

[1]: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25256

This reverts commit 21dcde096f.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25256>

meson.build

@@ -926,7 +926,6 @@ endforeach
 _attributes = [
   'const', 'flatten', 'malloc', 'pure', 'unused', 'warn_unused_result',
   'weak', 'format', 'packed', 'returns_nonnull', 'alias', 'noreturn',
-  'nonnull',
 ]
 foreach a : cc.get_supported_function_attributes(_attributes)
   pre_args += '-DHAVE_FUNC_ATTRIBUTE_@0@'.format(a.to_upper())