OpenZFS 1300 - filename normalization doesn't work for removes

Authored by: Kevin Crowe <kevin.crowe@nexenta.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/1300
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/8f1750d
Closes #5725

Porting notes:

• zap_micro.c: all MT_EXACT are replaced by 0