Deprecate --use-local-canvaskit flag

[harryterkelsen]

We should always use the locally-built CanvasKit in tests.

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[flutter-dashboard]

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[eyebrowsoffire]

This is actually subsumed by my changes here: #39984

It's going to be a lot easier to wait for that, since that simultaneously switches us over to the engine_v2 recipes, so you don't have to worry about coordinating stuff with the old web_engine recipe (which uses this flag, hence why you are getting CI failures here).

[flutter-dashboard]

This pull request executed golden file tests, but it has not been updated in a while (20+ days). Test results from Gold expire after as many days, so this pull request will need to be updated with a fresh commit in order to get results from Gold.

[kevmoo]

Are we deprecating or removing? Tis different. 😄

[eyebrowsoffire]

We're removing it. It's already gone with the web test reorganization, so we should just close this.