Removing Patch dependency for OpenBSD

This seemed to go along with the work in #1554. No available package provides the 'patch' binary:

```
[~/projects/shell-rvm] $> which patch
/usr/bin/patch
[~/projects/shell-rvm] $> pkg_info -E /usr/bin/patch
[~/projects/shell-rvm] $>
```

When using rvm-head, I consistently get missing dependency warnings without this. If there's additional improvements I missed re: this, I'll be happy to make them.