Remove MathOptInterface installation from CI

Removed the installation step for the MathOptInterface package from the CI workflow.

Author: blegat

.github/workflows/ci.yml

@@ -35,13 +35,6 @@ jobs:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
       - uses: julia-actions/cache@v2
-      - name: MOI
-        shell: julia --project=@. {0}
-        run: |
-          using Pkg
-          Pkg.add([
-              PackageSpec(name="MathOptInterface", rev="master"),
-          ])
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
       - uses: julia-actions/julia-processcoverage@v1