[Cashtab] Remove duplicated code

Summary:
Looks like an artifact from when we first started supported txs constructed from url params. At some point, this logic was moved, but this part of the code wasn't updated.

Remove this if/else block that resolves to the same thing.

Test Plan: npm test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15153