Remove unnecessary URI accessors from public api

[nothingmuch]

These accessors are only needed internally in the crate.

The receiver pubkey is still pub because payjoin-cli (as should other implementations) checks for reuse and uses the pubkey to uniquely identify sessions when resuming.

This is following up on @DanGould's observation, but I couldn't find the comment or even remember if it was in a call or on github.

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[coveralls]

Pull Request Test Coverage Report for Build 17775619793

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.709%

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Totals
Change from base Build 17773227581:	0.0%
Covered Lines:	8099
Relevant Lines:	9561

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💛 - Coveralls

[nothingmuch]

@arminsabouri or @spacebear21 i expect one of the integrations previously used or uses the endpoint method or it wouldn't be in the ffi interface, i'm assuming that wouldn't be a pain to live without but lmk if that's wrong please

[DanGould]

i expect one of the integrations previously used or uses the endpoint method or it wouldn't be in the ffi interface, i'm assuming that wouldn't be a pain to live without but lmk if that's wrong please

This was previously used to index the session by for resumption. If we're using receiver_pubkey for this, like we are in payjoin-cli, it may be removed.

[DanGould]

ACK 5b0b629