Revert "SUNRPC: Micro-optimise when the task is known not to be sleeping"

This reverts commit 009a82f6.

The ability to optimise here relies on compiler being able to optimise
away tail calls to avoid stack overflows. Unfortunately, we are seeing
reports of problems, so let's just revert.

Reported-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>