Remove reference to run-pass tests

Author: lnicola

src/tests/intro.md

@@ -26,9 +26,7 @@ that give more details.
 
 - [`ui`](./adding.html#ui) – tests that check the exact
   stdout/stderr from compilation and/or running the test
-- `run-pass` – tests that are expected to compile and execute
-  successfully (no panics)
-  - `run-pass-valgrind` – tests that ought to run with valgrind
+- `run-pass-valgrind` – tests that ought to run with valgrind
 - `run-fail` – tests that are expected to compile but then panic
   during execution
 - `compile-fail` – tests that are expected to fail compilation.