chore(spanner): remove injecting env

Author: harshachinta

.github/workflows/ci.yaml

@@ -86,8 +86,6 @@ jobs:
           distribution: temurin
       - run: echo "SUREFIRE_JVM_OPT=-Djvm=${JAVA_HOME}/bin/java" >> $GITHUB_ENV
         shell: bash
-      - run: echo "MAVEN_OPTS=-DGOOGLE_CLOUD_SPANNER_MULTIPLEXED_SESSIONS=true -DGOOGLE_CLOUD_SPANNER_MULTIPLEXED_SESSIONS_FOR_RW=true" >> $GITHUB_ENV
-        shell: bash
       - uses: actions/setup-java@v3
         with:
           java-version: 17