There are only two measurement systems that locales use: US and metric.
For the former, move to copying the en_US locale, while for the latter,
move to copying the i18n locale. This lets us clean up all the stray
comments like FIXME.
There should be no functional differences here.
There's no real value in populating this field when it's the same as the
default POSIX setting, so drop it from most locales so it's clear what's
going on.
repertoire maps and character mnemonics were used early in the glibc
i18n/l10n effort but were quickly deprecated in favor of Unicode code
points. According to ChangeLog, the in-tree repertoire maps were
removed 2000-07-07 but some stray references remain even today. The
patch below removes them.
