5-seconds test is not a reason for broken-smt-backend

We have several tests that take a lot longer, and test time is vastly
dominated by JBMC's tests anyway.

Author: tautschnig

regression/cbmc/Bitfields3/paths.desc

@@ -1,11 +1,8 @@
-CORE broken-smt-backend
+CORE
 main.c
 --pointer-check --bounds-check --paths lifo
 ^EXIT=0$
 ^SIGNAL=0$
 ^VERIFICATION SUCCESSFUL$
 --
 ^warning: ignoring
---
-This test is marked broken-smt-backend for performance reasons only: it passes,
-but takes 5 seconds to do so.