macOS: drop gcc option

I am currently working on revising and updating our macOS build scripts and encountered issue #1893 (closed). Reflecting on this, I questioned our current method of including a manual homebrew installation in our distribution. As the homebrew project doesn't officially support this, it extends the installation time unnecessarily, especially for those with slower internet connections. Additionally, having outdated versions of gcc on hand could potentially lead to security risks.

To my understanding, the primary reason for this inclusion is to facilitate the use of gcc for the use_dll option, as well as to accommodate users without admin privileges on their Mac. However, this approach seems contradictory since installing the pkg already requires admin rights because the files are installed into /Applications and the Command Line Tools installation also requires admin rights.

Therefore, I propose two main changes to our approach:

1. Eliminate the gcc option from the installer and instead, provide directions to users on how to install gcc using the homebrew project. Maybe an info box after the installation finishes. This will not only expedite the installation process but also eliminate potential issues linked with outdated brew versions in our directory.

2. Introduce a method to install the pkg without admin privileges, enabling it to be installed directly into the end-user's home directory without needing elevated privileges. This will, of course, require verification that Apple's Command Line Tools are installed (but it might actually be the case that MATLAB also installs them).

I believe these proposed adjustments will result in a more efficient installation process and better adherence to Homebrew's best practices. Any feedback on these proposed changes is welcome.