Bug 1239870 - Part 1: Remove declaration of test_utils from header. r=bwc

Once files are all compiled into the same gtest this will cause duplicate
symbol errors. It's also unused.

media/mtransport/test/mtransport_test_utils.h

@@ -101,11 +101,6 @@ class MtransportTestUtils {
 };
 
 
-MtransportTestUtils *mtransport_test_utils;
-
-#define SETUP_MTRANSPORT_TEST_UTILS() \
-  MtransportTestUtils utils_; mtransport_test_utils = &utils_
-
 #define CHECK_ENVIRONMENT_FLAG(envname) \
   char *test_flag = getenv(envname); \
   if (!test_flag || strcmp(test_flag, "1")) { \
@@ -115,4 +110,3 @@ MtransportTestUtils *mtransport_test_utils;
 
 
 #endif
-