fix: adjust signrawtransactionwithkey help text

[UdjinM6]

Issue being fixed or feature implemented

amount was introduced in #3101. Double checked the code and yes, we do pass it around (for compatibility reasons) but it doesn’t affect the sig right now, you can set it to 0 or just skip it completely so it should be optional, not required. We even have a test that uses signrawtransactionwithkey and ignores amounthttps://github.com/dashpay/dash/blob/master/test/functional/rpc_signrawtransaction.py#L19-L46.

NOTE: It might become required for sighashtype with SIGHASH_DIP0143 flag after #5860 activation.

kudos to @pshenmic for noticing

What was done?

Adjust help text

How Has This Been Tested?

Run tests

Breaking Changes

n/a

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation
• I have assigned this pull request to a milestone (for repository code-owners and collaborators only)

[PastaPastaPasta]

utACK