Revert "Run nightly bundler integration tests also with React 18 (#76606)"

This reverts commit f81ba18.

Author: bgw

.github/workflows/integration_tests_reusable.yml

@@ -86,16 +86,13 @@ jobs:
       fail-fast: false
       matrix:
         group: ${{ fromJSON(needs.generate-matrices.outputs.e2e) }}
-        # Empty value uses default
-        react: ['', '18.3.1']
     uses: ./.github/workflows/build_reusable.yml
     with:
       afterBuild: |
         # e2e and ${{ inputs.test_type }} tests with `node run-tests.js`
 
         export NEXT_TEST_CONTINUE_ON_ERROR=TRUE
         export NEXT_E2E_TEST_TIMEOUT=240000
-        export NEXT_TEST_REACT_VERSION=${{ matrix.react }}
         export NEXT_TEST_MODE=${{
           inputs.test_type == 'development' && 'dev' || 'start'
         }}
@@ -122,8 +119,6 @@ jobs:
       fail-fast: false
       matrix:
         group: ${{ fromJSON(needs.generate-matrices.outputs.integration) }}
-        # Empty value uses default
-        react: ['', '18.3.1']
     uses: ./.github/workflows/build_reusable.yml
     with:
       nodeVersion: 18.18.2
@@ -132,7 +127,6 @@ jobs:
 
         export NEXT_TEST_CONTINUE_ON_ERROR=TRUE
         export NEXT_E2E_TEST_TIMEOUT=240000
-        export NEXT_TEST_REACT_VERSION=${{ matrix.react }}
 
         # HACK: Despite the name, these environment variables are just used to
         # gate tests, so they're applicable to both turbopack and rspack tests