Reduce transactions for acquiring and releasing provider

App may access a provider frequently in a short time.
(Without using ContentProviderClient to keep the connection)
Then there will have some overhead for the management of
provider reference. So with a delay to release the provider,
the app can reuse the existing holder within the retain time.

Also change removeContentProvider to a one-way method to reduce
the time spent on app's main thread. This should be safe because
originally the app can acquire provider from any thread.

The cold start time of calendar app can be reduced by ~20ms.

Test: AppLaunchTest
Bug: 123043091
Change-Id: I220cec3deab18b658f4102f7eb9f47599c7c4b7c