LibUnicode: Use LibTimeZone's list of time zone names

LibUnicode no longer needs to generate a list of time zone names that it
parsed from metaZones.json. We can defer to the TZDB for a golden list
of time zones.

Userland/Libraries/LibUnicode/Forward.h

@@ -35,7 +35,6 @@ enum class ScriptTag : u8;
 enum class StandardNumberFormatType : u8;
 enum class Style : u8;
 enum class Territory : u8;
-enum class TimeZone : u16;
 enum class Weekday : u8;
 enum class WordBreakProperty : u8;