[Cashtab] Improve rendering of from contact name in tx history

Summary:
Current .map() implementation is just bad...will give you lots of empty spaces if you have a big contact list.

Simplify this and add a test.

Throw out the overcomplicated method of determining whether or not a tx is from a known address, which allows deletion of associated function and unit tests not used anywhere else.

Test Plan: npm test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15498