Ancient msgfmt doesn't know about generics.
This change allows devs to set javac.compilerargs=-Xlint:unchecked
in override.properties without getting an
overwhelming number of false positives from the bundles.
If msgfmt ever adds a --java5 option, we can remove this,
but it's been almost 20 years.
For the same reason, while the sed script is fragile,
seems unlikely msgfmt will change the output without a new option.
If they do, we'll fix it then.
f6e951e297