mime-construct: update runtime dependencies

Update runtime dependencies of mime-construct:

* drop WaitStat.pm and Signal.pm which are from libproc-waitstat-perl
  and its dependency libipc-signal-perl
* add patch to return 0 for option '--help'
* replace postfix with msmtp which is more lightweight
* add perl modules which are required for mime-construct to run

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>