chore(l10n): point workflow to look at correct folder

Because:

* L10n workflow to flag l10n reviewers to gettext changes fails silently because npx grunt script doesn't overwrite previously extracted files.

This commit:

* Removes files from target folder to ensure all changes in files are present.

.github/workflows/l10n-gettext-extract.yml

@@ -51,6 +51,7 @@ jobs:
 
           # Extract gettext
           cd ./packages/fxa-content-server
+          rm ./locale/templates/LC_MESSAGES/*
           npx grunt l10n-extract
           cd ../..