kmsplayerendpoint: Fix pad-removed callback

Appsrc is now gotten from sink pad of the appsink

Change-Id: Ic7c73a21c46b1add09d1c7fd41889da9d5a2ae7d
kmshttpendpoint: Force caps negotiation in appsrc using the fixed caps set in appsink through event caps

Change-Id: Iefd1a51d7d1a3e47131e185e90249887ea053113