Always OBJ_DESTRUCT the send request.

(cherry picked from commit 924d39e415e7df53841803941e450aa42b119650)
ob1: change an OPAL_UNLIKELY to OPAL_LIKELY

Per
https://github.com/open-mpi/ompi/commit/924d39e415e7df53841803941e450aa42b119650#commitcomment-8378266,
this OPAN_UNLIKELY should really be OPAL_LIKELY.

(cherry picked from commit 7a5b2e9b13eaa1d1f3514a52e1afa8c6ddafec70)
Merge pull request #66 from jsquyres/pr/ob1-destructor-fix-2

ob1 destructor fix #2