Updates PendingIntent-based service APIs

Modifies the APIs such that ContextHubClient can be generated by
either the ContextHubClientCallback or the PendingIntent (exclusive or),
for simplicity. ContextHubClients can be regenerated through the
createClient() API, while maintaining the original host endpoint ID.

Also removes the API implementation based on the original design.

Bug: 117612105
Test: Compile only
Change-Id: Ic62aa8695eee3d68722163934de76e77c1f0bc0c