intel/brw: Remove 'using namespace brw' directives

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33418>

src/intel/compiler/test_opt_combine_constants.cpp

@@ -8,8 +8,6 @@
 #include "brw_builder.h"
 #include "brw_cfg.h"
 
-using namespace brw;
-
 struct FSCombineConstantsTest : public ::testing::Test {
    FSCombineConstantsTest() {
       mem_ctx = ralloc_context(NULL);