Improve removal of other languages than fr-FR and en-US

Old hack doesn't work anymore
1 job for tedomum-french-only in 8 minutes and 21 seconds (queued for 12 seconds)
Status Job ID Name Coverage
  Build
failed #960
build

00:08:21

 
Name Stage Failure
failed
build Build
npm ERR! Failed at the peertube@2.1.0 build script.
npm
ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm
ERR! /home/peertube/.npm/_logs/2020-04-15T13_43_53_348Z-debug.log
The command '/bin/sh -c yarn install --pure-lockfile && npm run build -- $NPM_RUN_BUILD_OPTS && rm -r ./node_modules ./client/node_modules && yarn install --pure-lockfile --production && yarn cache clean' returned a non-zero code: 1
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit status 1