Technical Debt - Remove point & public key related in web backend since we didn't use it.

[chenchanglew]

web-backend will retrieve the private key and public key when they sign a request. However the public key is not used in this case, thus we can remove it.

Where:
web/backend/src/Server.tx app.delete()
web/backend/src/Server.tx getPayload()

Target:
all functions should have worked as before
pass all related unit tests and integration tests.