Remove JS and CSS asset compressors

[tom93]

TO DO:

• Test (update: did light testing, no issues)
• Compare size of assets before/after

Stacked on #308 and #309.

From the commit message:

Rails 8 has moved away from asset compression[1].

uglifier (JS compressor) requires a JavaScript runtime (which we
previously provided using mini_racer). It's a large install and raises
security concerns because it uses an outdated version of V8 (it's only
meant to run as part of asset precompilation, not in the running web
server; but still).

yui requires the Java Runtime Environment.

We follow the Rails 8 rationale and remove the asset compression (even
though we are still on a much older version of Rails).

[1] https://guides.rubyonrails.org/v8.0/asset_pipeline.html

[coveralls]

coverage: 37.631%. remained the same
when pulling 2d3f6d7 on remove-asset-compressors
into dd4df24 on master.

[bagedevimo]

While i'm fine with this in general I think it's worth at least briefly discussing what the plan for assets is before merging. Rails 8 ships importmaps by default but that's only really viable for those who don't care about backwards compatibility or compiling assets, which IMO isn't necessarily a great choice for a lot of applications.

[tom93]

Definitely.

I created this PR because I got annoyed with bundle install running out of RAM while testing Rails 5 (a VM with 1GB isn't enough, need to enable swap). No rush to merge, just created it so I won't forget and to start the investigation/discussion.

I assumed Uglifier was only compressing (not adding ES compat) and I was hoping everything would "just work" (but as I said I didn't even bother testing), do you have any particular concerns / things to test? I remember talking about importmaps for auto-updating jQuery, but I'm not sure why else we would need importmaps / non-trivial asset compilation.