patch 8.1.0785: depending on the configuration some functions are unused

Problem:    Depending on the configuration some functions are unused.
Solution:   Add more #ifdefs, remove unused functions. (Dominique Pelle,
            closes #3822)
diff --git a/src/ops.c b/src/ops.c
index 9ee2339..4b1040f 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -201,6 +201,7 @@
     return opchars[op][2] & OPF_LINES;
 }
 
+#if defined(FEAT_JOB_CHANNEL) || defined(PROTO)
 /*
  * Return TRUE if operator "op" changes text.
  */
@@ -209,6 +210,7 @@
 {
     return opchars[op][2] & OPF_CHANGE;
 }
+#endif
 
 /*
  * Get first operator command character.
@@ -1050,6 +1052,8 @@
 #endif
 }
 
+#if (defined(FEAT_CLIPBOARD) && defined(FEAT_X11) && defined(USE_SYSTEM)) \
+	|| defined(PROTO)
     void
 free_register(void *reg)
 {
@@ -1061,6 +1065,7 @@
     vim_free(reg);
     *y_current = tmp;
 }
+#endif
 
 #if defined(FEAT_MOUSE) || defined(PROTO)
 /*