btrfs: delete pointless BUG_ONs on extent item size

Checking extent item size in add_inline_refs() is redundant, we do that
already in tree-checker after reading the extent buffer and it won't
change under normal circumstances.  It was added long ago in
8da6d581 ("Btrfs: added btrfs_find_all_roots()") and does not seem
to have a clear purpose.

Similar case in extent_from_logical(), added in a542ad1b ("btrfs:
added helper functions to iterate backrefs").
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -1036,8 +1036,6 @@ static int add_inline_refs(struct btrfs_backref_walk_ctx *ctx,
 	slot = path->slots[0];
 
 	item_size = btrfs_item_size(leaf, slot);
-	BUG_ON(item_size < sizeof(*ei));
-
 	ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
 
 	if (ctx->check_extent_item) {
@@ -2256,7 +2254,6 @@ int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
 
 	eb = path->nodes[0];
 	item_size = btrfs_item_size(eb, path->slots[0]);
-	BUG_ON(item_size < sizeof(*ei));
 
 	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
 	flags = btrfs_extent_flags(eb, ei);