Fix testDumpsysCacheinfo() for Ravenwood

The ravenwood tests run in isolation so "well-known" caches are not
present.  This removes the check that a well-known cache exists.

Flag: EXEMPT bug-fix
Bug: 419264748
Test: atest
 * FrameworksCoreTests:PropertyInvalidatedCacheTests
Change-Id: If593d583caecd4089197828d655e2e382dc77fcc