Remove WebView-package-being-replaced logic from WebViewUpdateService.

The replacing-logic tries to handle packages being uninstalled while
being replaced. This can't be handled through listening to
package-replaced intents since those can be delivered long after the
actual problem occurs.

Bug: 27605997
Change-Id: Iba8e546a5bba1ceb6226d4edb71db088c81ae1a9