SUNRPC: Remove EXPORT_SYMBOL_GPL for svc_process_bc()

svc_process_bc(), previously known as bc_svc_process(), was
added in commit 4d6bbb62 ("nfs41: Backchannel bc_svc_process()")
but there has never been a call site outside of the sunrpc.ko
module.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/svc.c

@@ -1623,7 +1623,6 @@ void svc_process_bc(struct rpc_rqst *req, struct svc_rqst *rqstp)
 	WARN_ON_ONCE(atomic_read(&task->tk_count) != 1);
 	rpc_put_task(task);
 }
-EXPORT_SYMBOL_GPL(svc_process_bc);
 #endif /* CONFIG_SUNRPC_BACKCHANNEL */
 
 /**