Remove bad incompatible_use_toolchain_transition reference.

[gregestren]

Bazel doesn't recognize this as of bazelbuild/bazel@f53608a.

This causes @bazelbuild/examples CI failure: bazelbuild/examples#610.

Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: no

Test plan

• Covered by existing test cases
• Manual testing; please provide instructions so we can reproduce: see [Bazel Examples CI] Unable to find package local_config_platform  bazelbuild/examples#610.

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