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

This reverts commit 3996557ec61a6eeefaa3448480012205b8825374, reversing
changes made to 62102dd1f913a0ac43f4f8359999a571e09c11d9.

@wchen-r7 , please verify. 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.

Reverting this commit resolves the rspec tests, but now it's difficult to tell what was lost in the PRs you landed after f5d1d8eacee7e11255e02ae38c4780cf4f8a642a

Specifically, PR #2577 and #2544. Those may have to be redone.