workflows: static-checks: Remove TRAVIS_XXX variables

These variables are unused since we don't use travis CI. This also allows to
remove two steps:

- 'Setup GOPATH' only printed variables
- 'Setup travis reference' modified some shell local variables that don't have
  any influence on the rest of the steps

The TRAVIS var is still used by tools/osbuilder/tests to determine if
virtualization is available.

Fixes: #3544
Signed-off-by: Jeremi Piotrowski <jpiotrowski@microsoft.com>

.github/workflows/static-checks.yaml

@@ -20,9 +20,6 @@ jobs:
           - "sudo -E PATH=\"$PATH\" make test"
     env:
       TRAVIS: "true"
-      TRAVIS_BRANCH: ${{ github.base_ref }}
-      TRAVIS_PULL_REQUEST_BRANCH: ${{ github.head_ref }}
-      TRAVIS_PULL_REQUEST_SHA : ${{ github.event.pull_request.head.sha }}
       RUST_BACKTRACE: "1"
       target_branch: ${{ github.base_ref }}
     steps:
@@ -52,23 +49,11 @@ jobs:
           fi
           echo "Check passed"
         fi
-    - name: Setup GOPATH
-      if: ${{ !contains(github.event.pull_request.labels.*.name, 'force-skip-ci') }}
-      run: |
-        echo "TRAVIS_BRANCH: ${TRAVIS_BRANCH}"
-        echo "TRAVIS_PULL_REQUEST_BRANCH: ${TRAVIS_PULL_REQUEST_BRANCH}"
-        echo "TRAVIS_PULL_REQUEST_SHA: ${TRAVIS_PULL_REQUEST_SHA}"
-        echo "TRAVIS: ${TRAVIS}"
     - name: Set env
       if: ${{ !contains(github.event.pull_request.labels.*.name, 'force-skip-ci') }}
       run: |
         echo "GOPATH=${{ github.workspace }}" >> $GITHUB_ENV
         echo "${{ github.workspace }}/bin" >> $GITHUB_PATH
-    - name: Setup travis references
-      if: ${{ !contains(github.event.pull_request.labels.*.name, 'force-skip-ci') }}
-      run: |
-        echo "TRAVIS_BRANCH=${TRAVIS_BRANCH:-$(echo $GITHUB_REF | awk 'BEGIN { FS = \"/\" } ; { print $3 }')}"
-        target_branch=${TRAVIS_BRANCH}
     - name: Setup
       if: ${{ !contains(github.event.pull_request.labels.*.name, 'force-skip-ci') }}
       run: |