Update user's last login date within /login endpoint

[adarshm11]

After a user signs in src/APIFunctions/Auth.js:79. Their last login date is updated in a second API call from the browser. Updating the user's last login date should happen within the /login API.

game plan

• remove the updateLastLoginDate function in src/APIFunctions/User.js:149
• change /login in api/main_endpoints/routes/Auth.js:129 to not use else statements, instead returning early like

if (!user) {
  return res
    .status(UNAUTHORIZED)
    .send({
      message: 'Username or password does not match our records.'
    });
}
// down here you can assume the user exists and continue with the code in `else` outside of a nested block

• set the last login date in api/main_endpoints/routes/Auth.js:179
• do we have unit tests for the /login API, if so, can we add a check to make sure the user's last login date was updated?