[Cashtab] Remove superfluous tx history count param

Summary: This is doubled, now that we have pagination we only really care about the page size. We used this before because we combined tx history from multiple path addresses.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18681