patch 9.0.0063: too many type casts for dict_get functions

Problem:    Too many type casts for dict_get functions.
Solution:   Change the key argument from "char_u *" to "char *".
diff --git a/src/time.c b/src/time.c
index 4adcce5..dc8594a 100644
--- a/src/time.c
+++ b/src/time.c
@@ -863,7 +863,7 @@
 	    return;
 	}
 	if (dict_has_key(dict, "repeat"))
-	    repeat = dict_get_number(dict, (char_u *)"repeat");
+	    repeat = dict_get_number(dict, "repeat");
     }
 
     callback = get_callback(&argvars[1]);