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/evalvars.c b/src/evalvars.c
index 3d03ed8..f2128a6 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -2534,7 +2534,7 @@
     }
     else
     {
-	p = vim_strnsave(name, (int)len);
+	p = vim_strnsave(name, len);
 	if (p == NULL)
 	    return NULL;
     }