patch 8.2.0373: type of term_sendkeys() is unknown

Problem:    Type of term_sendkeys() is unknown.
Solution:   Just return zero. (closes #5762)
diff --git a/src/terminal.c b/src/terminal.c
index 34316d8..30590b6 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -5746,13 +5746,12 @@
  * "term_sendkeys(buf, keys)" function
  */
     void
-f_term_sendkeys(typval_T *argvars, typval_T *rettv)
+f_term_sendkeys(typval_T *argvars, typval_T *rettv UNUSED)
 {
     buf_T	*buf = term_get_buf(argvars, "term_sendkeys()");
     char_u	*msg;
     term_T	*term;
 
-    rettv->v_type = VAR_UNKNOWN;
     if (buf == NULL)
 	return;