Remove unnecessary casts from fast-import

Jeff King pointed out that these casts are quite unnecessary, as
the compiler should be doing them anyway, and may cause problems
in the future if the size of the argument for to_atom were to ever
be increased.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -1066,7 +1066,7 @@ static void load_tree(struct tree_entry *root)
 		if (!c)
 			die("Corrupt mode in %s", sha1_to_hex(sha1));
 		e->versions[0].mode = e->versions[1].mode;
-		e->name = to_atom(c, (unsigned short)strlen(c));
+		e->name = to_atom(c, strlen(c));
 		c += e->name->str_len + 1;
 		hashcpy(e->versions[0].sha1, (unsigned char*)c);
 		hashcpy(e->versions[1].sha1, (unsigned char*)c);
@@ -1227,7 +1227,7 @@ static int tree_content_set(
 	if (t->entry_count == t->entry_capacity)
 		root->tree = t = grow_tree_content(t, t->entry_count);
 	e = new_tree_entry();
-	e->name = to_atom(p, (unsigned short)n);
+	e->name = to_atom(p, n);
 	e->versions[0].mode = 0;
 	hashclr(e->versions[0].sha1);
 	t->entries[t->entry_count++] = e;