umass/quirk: Remove useless quirk for Transcend flash

I have several of these. They all work without these quirks (either the
auto quirk mechanism does the right thing, or a likely
soon-to-be-removed vendor catch-all does the right thing, or no probing
at all does the right hting).

Both PREVENT ALLOW and SYNCHRONIZE CACHE are (a) unimplemented but (b)
return the proper asc/ascq code so da just does the right thing, quirk
or no. This was a left-over from the days where you'd get scary error
messages, but we'd work just fine. Now that the scary error messages are
gone (and only a calm one under bootverbose), this can be deleted.

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