Fix //drake labels names in bindings/pydrake/...

[jwnimmer-tri]

Relates #6996.

I am PR'ing these changes in chunks. The plan is that once everything is converted, we'll add a deprecation warning to the 6996.bzl before finally removing it.

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This change is 

[jwnimmer-tri]

+(status: priority: low)
+@EricCousineau-TRI for all review, please.

[EricCousineau-TRI]

, with minor question about commit granularity.

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Reviewed 6 of 6 files at r1.
Review status: all files reviewed at latest revision, 1 unresolved discussion.

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a discussion (no related file):
BTW Is there a motivation for separating each directory into commits, versus just squashing these? There does not seem to be a functional separation between the commits.

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Comments from Reviewable

[jwnimmer-tri]

Review status: all files reviewed at latest revision, 1 unresolved discussion.

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a discussion (no related file):

Previously, EricCousineau-TRI wrote…

BTW Is there a motivation for separating each directory into commits, versus just squashing these? There does not seem to be a functional separation between the commits.

I think it makes rebasing a little bit easier. If there's a conflict, you just --skip and redo that one file from scratch.

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Comments from Reviewable