Remove unused interactive mode code path from install scripts

Summary

During review of !5958 (merged), @mkozono noted that probably no one uses the install script in interactive mode. The only ways to invoke it interactively are with weird, undocumented invocations.

We should remove the interactive code path from the install scripts if no one uses it.

Affected scripts

• support/install
• support/geo-install

Proposal

1. Confirm that interactive mode is not used (check CI pipelines, docs, etc.)
2. Remove the interactive code path (if [ $# -eq 1 ] branches) from both scripts
3. Update documentation if needed