Validate_utxo treats missing utxos as an error

[benalleng]

Missing utxo information should always be treated as an error, the flag we had also was always set to true so its seems not helpful to create a function arg to always be set to true.

This Pr is practice to figure out if I am doing commit messages and commit tests correctly

[coveralls]

Pull Request Test Coverage Report for Build 13016693385

Details

• 5 of 5 (100.0%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 78.496%

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Files with Coverage Reduction	New Missed Lines	%
payjoin/src/send/mod.rs	2	93.79%

Totals
Change from base Build 12968704432:	-0.03%
Covered Lines:	3643
Relevant Lines:	4641

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💛 - Coveralls

[DanGould]

tACK a66f00c 🚀

This is the way to MOVE!

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Next commit, I'm going to be more anal about the commit message. I'd like to see

• imperative mood in the first line
• Capitalization
• Punctuation in subsequent lines

Always treat missing utxo as validate_utxo error

Missing utxo information should always be treated as an error, not just when a boolean flag is set.
This flag was also always set to true in the codebase so it seems useless.