Minor: avoiding purely sync async functions

[jasnell]

As a general best practice, to avoid unnecessary performance cost, purely sync async functions should be avoided.

For instance, from https://github.com/covidgreen/covid-green-backend-api/blob/current/lib/server.js:

server.addHook('onSend', async (req, res) => {
    res.header('Cache-Control', 'no-store')
    res.header('Pragma', 'no-cache')
    res.header(
      'Strict-Transport-Security',
      `max-age=${config.security.hstsMaxAge}; includeSubDomains`
    )
  })

The hook function is not doing anything asynchronous and therefore should not be an async function:

server.addHook('onSend', (req, res, done) => {
    res.header('Cache-Control', 'no-store')
    res.header('Pragma', 'no-cache')
    res.header(
      'Strict-Transport-Security',
      `max-age=${config.security.hstsMaxAge}; includeSubDomains`
    )
    done()
  })

The anti-pattern of using async functions with sync code is seen several places throughout the code.