fix: removed deprecated simple transaction from logics & docs

[Alex-Werner]

Issue being fixed or feature implemented

In 0.13, simpleTransaction were introduced as a initial improvement over InstantSend (was limited to 4 inputs), now this limitation has been removed and simpleTransaction are gone.
This PR updates implementation and documentation.

What was done?

• docs: removed .isSimpleTransaction from typings
• fix: removed .isSimpleTransaction from Transaction
• docs: removed simple transaction documentation
• tests: removed isSimpleTransaction tests

How Has This Been Tested?

Using current test suite minus removed unit test.

Breaking Changes

• fix(Transaction): .isSimpleTransaction is removed

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

[thephez]

concept ACK

[shumkov]

👍