Fix indirect Enum test

This never actually checked for the right thing; the test happened to pass because the return
value from Class.forName, when stubbed, might be null, and the actual code notionally under
test was always unreachable. Since the test is only here to ensure we don't have an invariant
violation when using an Enum which is never instantiated, I just remove the relevant condition
from the test.

Author: smowton

jbmc/regression/jbmc/NondetEnumOpaqueReturn/test_indirect_enum_initalization.desc

@@ -1,8 +1,12 @@
 CORE
 indirect/IndirectVirtualCall.class
 --function indirect.IndirectVirtualCall.main
-function java::indirect\.TestEnum\.<clinit>:\(\)V$
 ^EXIT=10$
 ^SIGNAL=0$
 --
 ^Invariant check failed$
+--
+In this test the Enum usage is actually unreachable, as our stubbed version
+of Class.forName always returns exactly a java.lang.Object, which cannot be
+cast to an Enum type. The test serves only to check we don't throw an invariant
+violation when casting to an uninstantiated Enum type.