Revert "SUNRPC: Don't allow waiting for exiting tasks"

This reverts commit 14e41b16.

This patch breaks the LTP acct02 test, so let's revert and look for a
better solution.

Reported-by: Mark Brown <broonie@kernel.org>
Reported-by: Harshvardhan Jha <harshvardhan.j.jha@oracle.com>
Link: https://lore.kernel.org/linux-nfs/7d4d57b0-39a3-49f1-8ada-60364743e3b4@sirena.org.uk/


Cc: stable@vger.kernel.org # 6.15.x
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>