Remove rubocop and msftidy touchpoints (Electro)

This replicates PR rapid7#3639 for the staging/electro-release branch.

Rubocop replaces the default YAML library which makes development
testing difficult. It does not cause problems on Travis, but according
to reports, it does cause instability with many individual dev
environments.

While I would love to have a more solid source of this bug report, right
now this was an oral report from @shuckins-r7 (who I tend to believe a
lot).

(Conflict resolved on rubocop.yml)

## Verification

- [x] `gem uninstall rubocop`
- [x] Run `tools/msftidy.rb modules/exploits/windows/smb/psexec.rb`
- [x] See no rubocop reports or errors.