patch 8.1.1384: using "int" for alloc() often results in compiler warnings

Problem:    Using "int" for alloc() often results in compiler warnings.
Solution:   Use "size_t" and remove type casts.  Remove alloc_check(), Vim
            only works with 32 bit ints anyway.
diff --git a/src/gui_w32.c b/src/gui_w32.c
index 5961830..bf27386 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -3120,9 +3120,9 @@
     charset_name = charset_id2name((int)lf.lfCharSet);
     quality_name = quality_id2name((int)lf.lfQuality);
 
-    res = (char *)alloc((unsigned)(strlen(font_name) + 30
+    res = (char *)alloc(strlen(font_name) + 30
 		    + (charset_name == NULL ? 0 : strlen(charset_name) + 2)
-		    + (quality_name == NULL ? 0 : strlen(quality_name) + 2)));
+		    + (quality_name == NULL ? 0 : strlen(quality_name) + 2));
     if (res != NULL)
     {
 	p = res;
@@ -7718,7 +7718,7 @@
 	}
 
 	/* Allocate menu label and fill it in */
-	text = label = alloc((unsigned)len + 1);
+	text = label = alloc(len + 1);
 	if (label == NULL)
 	    break;