remove gem update step on dockerfile

[yuenmichelle1]

Fixes broken Docker builds due to newest version of gem update compatible with Ruby 3.0 and we're on 2.7.

I don't think we need this step until we go from 2.7 -> 3.0 (See Slack thread )

Looking at diffs/git blame that step was added when we bumped from 2.6 -> 2.7.

ERROR ON CURRENT DOCKER BUILD

 > [ 7/10] RUN gem i "rubygems-update:<3.5.3" --no-document && update_rubygems:                                                                 
#11 35.12 ERROR:  Error installing rubygems-update:                                                                                             
#11 35.12       The last version of rubygems-update (< 3.5.3) to support your Ruby & RubyGems was 3.4.22. Try installing it with `gem install rubygems-update -v 3.4.22`
#11 35.12       rubygems-update requires Ruby version >= 3.0.0. The current ruby version is 2.7.8.225.

• As opposed to going to 3.0 willy nilly, I'm pretty sure we as a team would want to do a Dual boot of current app on 2.7 and then dual booted app on 3.0 to see if there are any breaking changes.

Review checklist

• First, the most important one: is this PR small enough that you can actually review it? Feel free to just reject a branch if the changes are hard to review due to the length of the diff.
• If there are any migrations, will they the previous version of the app work correctly after they've been run (e.g. the don't remove columns still known about by ActiveRecord).
• If anything changed with regards to the public API, are those changes also documented in the apiary.apib file?
• Are all the changes covered by tests? Think about any possible edge cases that might be left untested.