Fix translations detection for BCP 47 locales.

Drop BCP 47 unicode locale extension when passing the locale
into ICU ULocale.addLikelySubtags. Currently addLikelySubtags
discards region code for locales with extensions, making them
treated as not translated by Setup Wizard.

Test: manual run with debug logs.
Bug: 72336416

Change-Id: I7258577253486162b310e4102669db082cd09594