Revert "fs: check FMODE_LSEEK to control internal pipe splicing"

This reverts commit fd0a6e99b61e6c08fa5cf585d54fd956f70c73a6.

Which was upstream commit 97ef77c5.

The commit is missing dependencies and breaks NFS tests, remove it for
now.

Reported-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>