Revert "Fix conflcit lib/msf/util/exe.rb"

This was causing build failures:

https://travis-ci.org/rapid7/metasploit-framework/builds/13816889

It looks like there were a whole bunch of changes that weren't intended.

This reverts commit 3996557ec61a6eeefaa3448480012205b8825374, reversing
changes made to 62102dd1f913a0ac43f4f8359999a571e09c11d9.
Land #2624 - Fix broken rspec