Remove SPUURLRequest class

[zorgiepoo]

This class was only introduced because older OS versions we no longer support didn't have NSURLRequest support NSSecureCoding. Apple's documentation implies this was supported from macOS 10.9 onwards.

Fixes #2124

Misc Checklist:

• My change requires a documentation update on Sparkle's website repository
• My change requires changes to generate_appcast, generate_keys, or sign_update

Only bug fixes to regressions or security fixes are being backported to the 1.x (master) branch now. If you believe your change is significant enough to backport, please also create a separate pull request against the master branch.

Testing

I tested and verified my change by using one or multiple of these methods:

• Sparkle Test App
• Unit Tests
• My own app
• Other (please specify)

Tested that network service type, http headers, timeout interval, URL, cache policy are all preserved through a test app which encoded/decoded NSURLRequest object via NSSecureCoding on macOS 10.10.5 (VM) and macOS 12.4.

Tested that Test App still works normally. Tested another sample app using downloader XPC Service still works.

Interesting to note: one of the NSURLRequest properties isn't encoded/decoded properly on macOS 10.9, but that doesn't matter now.

macOS version tested:
12.4 (21F79)
10.10.5 (14F27) VM