[Cashtab] Delete unused utils

Summary: These files were perhaps used once upon a time but they are not used any longer. Delete them.

Test Plan:
npm test

grep -r debounce src no output
grep -r retry src and 1 match, in a comment

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15594