Hivex: regedit/hivexml not working

[Amar1729]

Two of hivex's targets are having problems building:

• [ ] hivexml (see errors i dealt with in this pr)
• [ ] hivexregedit. I found PERL errors with the formula, but can't figure out the proper write_env_script invocation, so have removed it from the formula's build (for now) https://github.com/Amar1729/homebrew-libguestfs/commit/166021c28051e3d224157d89654b91ab2aeba3fd