Revert "tests: Avoid Meson's strict TAP parsing for now"

Now that our error messages are valid UTF-8, we should no longer need to
do this.

This reverts commit 242e9893e7.

Signed-off-by: Simon McVittie <smcv@collabora.com>

tests/meson.build

@@ -183,6 +183,7 @@ foreach testcase : c_tests
       args : [exe],
       depends : runtime_repo,
       env : test_env,
+      protocol : 'tap',
       timeout : options.get('timeout', 30),
     )
   endif