cfg_rpc: fix typo

Thanks, lintian
> I: kamailio: spelling-error-in-binary usr/lib/x86_64-linux-gnu/kamailio/modules/cfg_rpc.so Delte Delete

src/modules/cfg_rpc/cfg_rpc.c

@@ -642,7 +642,7 @@ static void rpc_add_group_inst(rpc_t* rpc, void* c)
 }
 
 static const char* rpc_del_group_inst_doc[2] = {
-	"Delte an instance of a configuration group",
+	"Delete an instance of a configuration group",
 	0
 };