Revert "Switch to a build variant config instead of magic env vars (#2498)" (#2520)

.github/workflows/build_prepare.yaml

@@ -85,11 +85,6 @@ jobs:
               if: steps.branch-matching.outcome == 'failure' || steps.branch-matching.outcome == 'skipped'
               run: yarn run fetch --noverify -d ${{ inputs.config }} ${{ inputs.version }}
 
-            - name: Copy variant config
-              run: cp "$CONFIG_DIR/build.json" variant.json
-              env:
-                  CONFIG_DIR: ${{ inputs.config }}
-
             # We split this out to save the build_* scripts having to do it to make use of `hashFiles` in the cache action
             - name: Generate cache hash files
               run: |
@@ -175,4 +170,3 @@ jobs:
                       electronVersion
                       hakHash
                       changelog.Debian
-                      variant.json