arrow

GH-38088: [R] Remove outdated references to brew and autobrew (#38089)

### Rationale for this change

We no longer use autobrew to install on MacOS, so we no longer need CI jobs or helper scripts that had previously been referenced from this install path.

### What changes are included in this PR?

This PR removes references to autobrew that are no longer needed. It also removes the R homebrew CI job, which has been failing for several months. We had supported homebrew because `brew install apache-arrow --HEAD` was one method of avoiding a full binary install for potential MacOS contributors; however, downloading nightly static libraries (e.g., #38080) is an even faster way to get a compatible libarrow built for the R package and works on MacOS, Windows, and Linux.

### Are these changes tested?

These changes remove tests and infrastructure that are no longer relevant.

### Are there any user-facing changes?

No.
* Closes: #38088

Authored-by: Dewey Dunnington <dewey@voltrondata.com>
Signed-off-by: Jacob Wujciak-Jens <jacob@wujciak.de>