Revert r279011:
tdelete(3): don't delete the node we are about to return.

The original change, from NetBSD, was bogus; introduced a memory
leak and and broke POSIX. By reverting we actually match NetBSD's
latest revision.

This is a revert of the original merge: this function was rewritten
in 11-current.

Reported by: Markiyan Kushnir
Obtained from: NetBSD (CVS rev. 1.7, 1.8)