Remove rules for variables.css files

[tomdye]

Type: bug / feature

The following has been addressed in the PR:

• There is a related issue
• All code has been formatted with prettier
• Unit or Functional tests are included in the PR

Description:

Removes special rules for variables.css files.

Work towards: dojo/framework#683

[codecov]

Codecov Report

Merging #30 into master will not change coverage by %.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #30   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files           5       5           
  Lines         159     157    -2     
  Branches       20      20           
======================================
+ Misses        159     157    -2     

Impacted Files	Coverage Δ
src/webpack.config.ts	0.00% <ø> (ø)

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