Revert "dm thin: fix deadlock when swapping to thin device"

This reverts commit 84e13235 which is
commit 9bbf5feecc7eab2c370496c1c161bbfe62084028 upstream.

It is not needed as the commit it fixes was already reverted from the
android-4.19-stable branch.

Fixes: 84e13235 ("dm thin: fix deadlock when swapping to thin device")
Change-Id: I6ba31fef9123cbdfd131372463c90975618fa314
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>