root: Remove redundant patch.

The patch was required for `HEAD` builds when building with the Cocoa GUI backend. This patch has [now been applied](https://sft.its.cern.ch/jira/browse/ROOT-6297) to the `HEAD` and the `v5-34-00-patches branch`, so no longer needs to be applied by Homebrew.

Before this commit, users installing with `brew install root --HEAD` would see an error.

```
==> Cloning https://github.com/root-mirror/root.git
Updating /Library/Caches/Homebrew/root--git
==> Checking out branch v5-34-00-patches
==> Downloading https://gist.githubusercontent.com/veprbl/9ab33daa07b68c28671c/raw/31317dfa11eba19595207dc32851a1bb2d836b0a/gistfile1.txt
Already downloaded: /Library/Caches/Homebrew/root--patch-6d8625fd63fce92976e27248e4ad3698741e7eba.txt
==> Patching
patching file configure
Hunk #1 FAILED at 2655.
1 out of 1 hunk FAILED -- saving rejects to file configure.rej
patch unexpectedly ends in middle of line
Error: Failure while executing: /usr/bin/patch -g 0 -f -d /private/tmp/root-AMzw -p1 -i /private/tmp/root--patch-zaBU/gistfile1.txt
```

Both the current stable version, `v5-34-18`, and the `v5-34-00` patches branch now build successfully.