Travis: Unbreak the builds.

In the hopes of future-proofing as much as possible, jump to the latest
distribution Travis supports.

test/src/test.c

@@ -232,16 +232,3 @@ p_test_fail(const char *prefix, const char *message) {
 	malloc_cprintf(NULL, NULL, "%s%s\n", prefix, message);
 	test_status = test_status_fail;
 }
-
-void
-strncpy_cond(void *dst, const char *src, bool cond) {
-	if (cond) {
-		/*
-		 * Avoid strcpy and explicitly set length to 0 because the
-		 * `stringop-overflow` check may warn even if the specific test
-		 * is unreachable.
-		 */
-		size_t n = cond ? strlen(src) + 1 : 0;
-		strncpy(dst, src, n);
-	}
-}