Remove url from payjoin-ffi in favor of native payjoin::url

[benalleng]

Closes #1905

This removes the url dep in payjoin-ffi in favor of using the native payjoin url. I feel like there was a reason we told ourselves why we didn't want this at first but I can't find it for the life of me so I thought I should just put it out into the wild to see what we think.

I also notices there were some pretty egregious test errors where we were using url parsing instead of uri parsing.

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[coveralls]

Coverage Report for CI Build 36194121045

Coverage remained the same at 86.869%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	17013
Covered Lines:	14779
Line Coverage:	86.87%
Coverage Strength:	333.85 hits per line

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💛 - Coveralls

[DanGould]

seems like a simple oversight that got forgotten to be removed to me