chore: remove transitional toolchain transition parameter

[pjjw]

this parameter, intended for a long-applied behavior change in transitions, is gone in bazel 9 and causes analysis failure. remove it.

[aspect-workflows]

Test (Bazel 7.x) (Test)

All tests were cache hits

5 tests (100.0%) were fully cached saving 1m 19s.

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Test (Bazel 8.x) (Test)

All tests were cache hits

5 tests (100.0%) were fully cached saving 1m 48s.

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Test (Bazel 6.x) (Test)

e2e/smoke

All tests were cache hits

1 test (100.0%) was fully cached saving 37ms.

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Test (Bazel 7.x) (Test)

e2e/smoke

All tests were cache hits

1 test (100.0%) was fully cached saving 32ms.

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Test (Bazel 8.x) (Test)

e2e/smoke

All tests were cache hits

1 test (100.0%) was fully cached saving 63ms.