test-capability: drop work-around initialization

Since those workarounds have been added, work has been done to tighten
up log_*() return values. Seems we get no warning with
gcc-11.1.1-1.fc34.x86_64 and -O0/-O2.

src/test/test-capability.c

@@ -248,7 +248,7 @@ static void test_ensure_cap_64bit(void) {
 }
 
 int main(int argc, char *argv[]) {
-        bool run_ambient = false;  /* avoid false maybe-uninitialized warning */
+        bool run_ambient;
 
         test_setup_logging(LOG_INFO);