Consider removing support for ftp proxy from capabilities

[lutien]

Firefox doesn't support ftp protocol since version 90, Chrome since version 95, not sure about Safari. Firefox already doesn't support ftp proxy with WebDriver Classic (and BiDi), so we could consider if we want to remove support for it from the specification.

[whimboo]

@gsnedders would you mind giving feedback regarding the Safari status? As it looks like by this post it was all marked deprecated a long time ago, but it's not that clear when it was removed. Maybe in Safari 14 which came with macOS 10.13?

[gsnedders]

I don't believe we ever supported FTP proxies configured via WebDriver (and we don't support configuring proxies via WebDriver at all).

https://commits.webkit.org/242010@main is the commit that disabled FTP support in Safari by default, which appears to be Safari 15.4, based on the tags.

[whimboo]

Based on feedback on w3c/webdriver-bidi#932 (comment) and following comments there are no objections in getting FTP support removed. I'll go ahead and merge both pull requests. Web-platform tests will be updated via https://bugzilla.mozilla.org/show_bug.cgi?id=1972670.

[whimboo]

Both PRs for WebDriver classic and BiDi have been merged.