Remove ignores that are not ignoring anything

[goderbauer]

In preparation for dart-lang/sdk#35234.

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[flar]

I'm perplexed about these changes.

Aren't the "ignore unnecessary null comparison" comments a reminder that we should remove the assert statements at some point because once NNBD becomes a mandatory requirement rather than an optional choice then they are really vestigial.

Haven't we reached that point? Isn't NNBD the mandatory the default yet? If not, shouldn't we leave the comments to draw our attention to the unnecessary asserts later? If so, then why aren't we removing the vestigial asserts instead of removing the comments?

[goderbauer]

Aren't the "ignore unnecessary null comparison" comments a reminder that we should remove the assert statements at some point because once NNBD becomes a mandatory requirement rather than an optional choice then they are really vestigial.

The "unnecessary null comparison" lint has been turned off for the entire project here:

engine/analysis_options.yaml

Lines 37 to 38 in d6f6e69

	# Turned off until null-safe rollout is complete.
	unnecessary_null_comparison: ignore

So the line-based ignores are no longer necessary (and once dart-lang/sdk#35234 is resolved no longer allowed). Once we are ready to drop non-NNBD support, we can enable the lint again on the project level and it will tell us about all the lines that can now be removed.

Haven't we reached that point? Isn't NNBD the mandatory the default yet?

No, apps can (and many (most?) in the wild still do) run without NNBD enabled. In that mode we still need the asserts.