Use correct contains method in PermissionManagerService.

Hashtable#contains(String) is actually pre-generics method that maps to
Hashtable#containsValue(V). In this case, PermissionManagerService
actually wants to know if it contains a given key as the values in the
map are not Strings at all.

Bug: 217923092
Test: errorprone build
Change-Id: I1f315d1051aaab3831eaca34e12fc9858ee9aeda