ARM: Remove prototype of non-existent NaClGetThreadCombinedDescriptor()
ARM: Remove prototype of non-existent NaClGetThreadCombinedDescriptor()

Do the same for NaClSetThreadCombinedDescriptor().

Also remove forward struct declarations that are no longer needed.

BUG=none
TEST=build

Review URL: https://chromiumcodereview.appspot.com/10919217

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@9711 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client