patch 8.1.1393: unnecessary type casts

Problem:    Unnecessary type casts.
Solution:   Remove type casts from alloc() and lalloc() calls. (Mike Williams)
diff --git a/src/misc2.c b/src/misc2.c
index ddb677c..70b23e7 100644
--- a/src/misc2.c
+++ b/src/misc2.c
@@ -1290,7 +1290,7 @@
 {
     char_u	*p;
 
-    p = alloc((size_t)(len + 1));
+    p = alloc(len + 1);
     if (p != NULL)
     {
 	STRNCPY(p, string, len);