[Cashtab] Remove obsolete SendToken snapshot tests and replace with existing validation integration tests

Summary:
Depends on D15203

The new integration tests in SendTokenValidation.test.js are more comprehensive than the legacy snapshot test approach of SendToken.js.

SendTokenValidation.js is incomplete, but that is where all new integration tests for the SendToken component should go.

Delete the legacy snapshot test and rename SendTokenValidation.test.js to SendToken.test.js

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15207