[mercurial] Plan to remove obsolete files from l10n-central repositories

[Francesco Lodolo [:flod]]

Hi everyone,
Quick heads up: in the coming hours I plan to run a script to remove
obsolete files from l10n-central repositories.
If you work on Pontoon, this will have no practical effect. If you're
interested in the technical details, feel free to read on ;-)

Our l10n-central repositories accumulated a lot of obsolete files over time:
* Pontoon doesn't remove a file when it's removed from en-US.
* Pootle used to commit files with only comments and empty lines.

For the past two cycles, close to merge day I've run a script to remove
specific files that became obsolete, e.g.
https://hg.mozilla.org/l10n-central/af/rev/1e0a64d71bb7

The script is only going to remove .dtd, .properties, .ftl, .ini, .inc
that are either empty (no strings) or not available in gecko-strings.
It's not going to touch other type of files like READMEs or dictionaries.

I've already run the script on about a dozen locales, without noticing
any data loss
https://hg.mozilla.org/l10n-central/en-ZA/rev/e4daba5a57be

If you notice anything strange, please comment in this bug
https://bugzilla.mozilla.org/show_bug.cgi?id=1443175

Francesco