[backport#17553] wallet: Remove out of date comments for CalculateMaximumSignedTxSize
[backport#17553] wallet: Remove out of date comments for CalculateMaximumSignedTxSize

Summary:
6a2e6b0600077e5903400dc74bc8b0c26592fde6 Remove out of date comments for CalculateMaximumSignedTxSize (Gregory Sanders)

Pull request description:

  These paths can be hit for probably a number of reasons, and ISMINE spendability is not a requirement to call it.

  For example: During watch-only transaction creation, previous transaction in wallet, pubkey imported, but not the witnessscript associated with the prevout.

  In this case I think no/minimal comment is better than specific and soon to be out of date.

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Backport of Core [[https://github.com/bitcoin/bitcoin/pull/17553 | PR17553]]

Test Plan:
  read them

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7692

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