macOS install: remove bad ARM toolchains

[fauxpark]

Description

All of these will conflict with the ARM toolchain that the qmk formula specifies as a dependency (osx-cross/arm/arm-none-eabi-gcc@8). This should help users who've accidentally installed the wrong one as they just need to rerun qmk setup or the install script directly instead of messing around with brew to manually uninstall the "bad" formulae.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).