[alias-server] change function name getAllAliasTxs to getAliasTxs

Summary:
T3060

In prep for implementing incremental tx processing, change function name getAllAliasTxs to getAliasTxs. Then function can take an arbitrary amount of tx history and return all alias txs (i.e. all txs with correct prefix, fee, format -- txs that could be valid registrations assuming no prior conflicting registration).

Test Plan:
grep -r getAllAliasTxs . and no output (except mb an artifact left in node_modules cache)
npm test

Reviewers: #bitcoin_abc, Fabien, emack

Reviewed By: #bitcoin_abc, Fabien, emack

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13518