Remove outdated comment on test

Author: jezhiggins

regression/goto-analyzer/value-set-function-pointers-simple/test.desc

@@ -21,6 +21,3 @@ main.c
 ^main::1::fun3_show \(\) -> \{\[0\] = value-set-begin: .*ptr ->\(h\).* :value-set-end
 ^fun_global_show \(\) -> value-set-begin: .*ptr ->\(h\).* :value-set-end
 --
-These TOP values in the sets shouldn't exist.
-They're caused by a quirk in the implementation, see
-https://github.com/diffblue/cbmc/issues/5307 which has been filed to fix this bug.