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/edit.c b/src/edit.c
index 8a008cb..6e2fdb8 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -1943,7 +1943,7 @@
 	{
 	    curwin->w_cursor.col = (colnr_T)new_cursor_col;
 	    i = (int)curwin->w_virtcol - vcol;
-	    ptr = alloc((unsigned)(i + 1));
+	    ptr = alloc(i + 1);
 	    if (ptr != NULL)
 	    {
 		new_cursor_col += i;