datastores: Audit ast_channel_datastore_remove usage.

Audit of v1.8 usage of ast_channel_datastore_remove() for datastore memory
leaks.

* Fixed leaks in app_speech_utils and func_frame_trace.

* Fixed app_speech_utils not locking the channel when accessing the
channel datastore list.

Review: https://reviewboard.asterisk.org/r/3859/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@419684 f38db490-d61c-443f-a65b-d21fe96a405b