[l10n] Removal of obsolete strings and files

[peiying2]

Description

Let's plan on removing some old files no longer in use. We also need to set a cadence in removing obsolete strings.

• Old files
  We had a few new pages added last year with *[-2023](https://github.com/search?q=repo%3Amozilla-l10n%2Fwww-l10n+path%3A%2F%5Een%5C%2F%2F+2023&type=code) in the file names. Some of these were brand new files, while others were replacement of an older versions of the same pages.

The old files may not be limited to these. Please conduct an inventory check. Not only they are removed on Bedrock, they need to be removed in the www-l10n repo. We need a list of these file names so we can do the same on our end.

Additionally, please check pontoon.toml file to make sure it's updated accordingly.

-Obsolete strings
Last year Reem made a dent on this because of product name change. Can we make this more of a routine task to remove old strings from the files? Once every two or three months whatever cadence we can agree on.

[peiying2]

@stephaniehobson per our discussion.