[ecash-herald] Only use others if more than 1 others

Summary:
T2972

Say "and 1 other" if there is only 1 other recipient, otherwise "and n others"

Test Plan:
npm test (this changed mocks of sample blocks, covering this change)

npm run sendMsgByBlock 798881 output is pictured

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14174