remove mill support (#2)

.github/workflows/test.yml

@@ -45,24 +45,6 @@ jobs:
       - name: Binary compatibility
         run: sbt ++${{ matrix.scala }} mimaReportBinaryIssues
 
-  mill:
-    name: Mill Sanity Check
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        scala: [2.13.10, 2.12.17]
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v2
-      - name: Setup Scala
-        uses: olafurpg/setup-scala@v10
-      - name: Cache
-        uses: coursier/cache-action@v5
-      - name: Setup Mill
-        uses: jodersky/setup-mill@v0.2.3
-      - name: Mill sanity check
-        run: mill _[${{ matrix.scala }}].compile
-
   # TODO find better way to express Ops and AddNot as single test
   equiv:
     name: formal equivalence
@@ -99,7 +81,7 @@ jobs:
   # When adding new jobs, please add them to `needs` below
   all_tests_passed:
     name: "all tests passed"
-    needs: [test, mill, equiv]
+    needs: [test, equiv]
     runs-on: ubuntu-latest
     steps:
       - run: echo Success!