Remove postcss-preset-env dependency

[n-lark]

Description

We don't use this package so I am murdering it. Noticed this while reviewing build(deps-dev): bump postcss-preset-env from 9.3.0 to 11.3.2 #7620 - instead of upgrading we should just remove.

Related Issue(s)

N/A

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.47%. Comparing base (b9abc31) to head (a6d0267).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7636   +/-   ##
=======================================
  Coverage   76.47%   76.47%           
=======================================
  Files         413      413           
  Lines       21775    21775           
  Branches     5736     5736           
=======================================
  Hits        16652    16652           
  Misses       5123     5123           

Flag	Coverage Δ
backend	76.47% <ø> (ø)

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[knolleary]

Approved, but not sure what has triggered Trivy to start complaining.

[n-lark]

@knolleary Trivy just gets overwhelmed with the bigger diffs, I've been here before with the minmatch stuff and it was just a hiccup.