docs(tap-core): update rav and receipt constructors to remove outdate…

[ColePBryan]

…d information

signing has been moved to be handled in eip_712_signed_message struct and no longer happens in the constructor of RAV and Receipt. The documentation was not updated when the change happened. This commit corrects that information.

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🤖 Cargo Audit Report 🤖

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Pull Request Test Coverage Report for Build 5659603867

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.689%

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Totals
Change from base Build 5615738906:	0.0%
Covered Lines:	1027
Relevant Lines:	1242

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