patch 8.2.0967: unnecessary type casts for vim_strnsave()

Problem:    Unnecessary type casts for vim_strnsave().
Solution:   Remove the type casts.
diff --git a/src/ops.c b/src/ops.c
index 8f31deb..a681df0 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -1616,7 +1616,7 @@
 	if (pre_textlen >= 0
 		     && (ins_len = (long)STRLEN(firstline) - pre_textlen) > 0)
 	{
-	    ins_text = vim_strnsave(firstline, (int)ins_len);
+	    ins_text = vim_strnsave(firstline, ins_len);
 	    if (ins_text != NULL)
 	    {
 		// block handled here