Remove payments.ftl files

[bcolsson]

Since the removal of deprecated settings package from FXA in #1047 the resource .ftl files need to be removed.

We should wait for mozilla/pontoon#3965 to complete before doing this removal work however so we can preserve attribution for the removed strings.

[StaberindeZA]

@bcolsson it should be payments.ftl that's getting deprecated, not settings.ftl.

[bcolsson]

Thanks @StaberindeZA ! That's what my brain meant to write, but glad we caught this before I amputated the wrong limb 💦