Remove dead internal class ClearableSynchronizedPool

Summary:
`ClearableSynchronizedPool` (an `internal` Kotlin class in `ReactAndroid/.../common/`) was a variant of androidx `Pools.SynchronizedPool` adding a `clear()` method, but it was never instantiated or referenced anywhere. The live event pools (`OnLayoutEvent`, `PointerEvent`, `TouchEvent`, `ScrollEvent`) use androidx `SynchronizedPool` directly. This removes the orphaned class.

Changelog: [Internal]

Differential Revision: D108012905

Author: sammy-SC