Remove the hidden API "onRemoteCapabilityRequest" from the exposed interface...

Remove the hidden API "onRemoteCapabilityRequest" from the exposed interface CapabilityExchangeEventListener

The interface CapabilityExchangeEventListener is exposed.
However the API "onRemoteCapabilityRequest" is hidden and it will cause it cannot be implemented.
Remove this api for now and add it back when the api is ready to exposed.

Bug: 177451691
Test: atest CtsSystemApiSignatureTestCases:android.signature.cts.api.system.SignatureTest#testSignature
Change-Id: I9ac1b8a5654fe16b9ae862d6e65aec9319cb6be5