Revert "ext4: add new pending reservation mechanism"

This reverts commit 9bacbb4c which is
commit 1dc0aa46e74a3366e12f426b7caaca477853e9c3 upstream.

Eric writes:
	I recommend not backporting this patch or the other three
	patches apparently intended to support it to 4.19 stable.  All
	these patches are related to ext4's bigalloc feature, which was
	experimental as of 4.19 (expressly noted by contemporary
	versions of e2fsprogs) and also suffered from a number of bugs.
	A significant number of additional patches that were applied to
	5.X kernels over time would have to be backported to 4.19 for
	the patch below to function correctly. It's really not worth
	doing that given bigalloc's experimental status as of 4.19 and
	the very rare combination of the bigalloc and inline features.

Link: https://lore.kernel.org/r/Y8mAe1SlcLD5fykg@debian-BULLSEYE-live-builder-AMD64


Cc: Eric Whitney <enwlinux@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>