monitor: Move qmp_query_qmp_schema to qmp-cmds-control.c

monitor: Move qmp_query_qmp_schema to qmp-cmds-control.c

monitor/misc.c contains code that works only in the system emulator, so
it can't be linked to tools like a storage daemon. In order to make
schema introspection available for tools, move the function to
monitor/qmp-cmds-control.c, which can be linked into the storage daemon.

Signed-off-by: Kevin Wolf <[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>
Message-Id: <20200129102239[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>