chore(ci): remove unneeded permissions from system-tests subworkflow

Author: nccatoni

.github/workflows/run-system-tests.yaml

@@ -64,9 +64,7 @@ jobs:
     # If you change the following comment, update the pattern in the update_system_test_reference.sh script to match.
     uses: DataDog/system-tests/.github/workflows/system-tests.yml@main # system tests are pinned on release branches only
     permissions:
-      contents: read
       id-token: write
-      packages: write
     with:
       library: java
        # If you change the following comment, update the pattern in the update_system_test_reference.sh script to match.