Remove CacheManager related tests

CacheManager will not be implemented in webviewchromium and its
implementation has been removed from WebViewClassic. So removing
CacheManager related tests.

There is no way to test WebView.clearCache in isolation without
CacheManager implementation, so removing that test as well. Note that
clearCache is tested in the test for BlockNetworkLoads.

Change-Id: Ib503ab6b51310a4a9b8a8c6995a95a274e6be861