pidgin/pidgin

Drop PidginCredentialProviderStore.

2021-05-13, Elliott Sales de Andrade
17208bd7a906
Drop PidginCredentialProviderStore.

It's no longer needed now that the prefs use a `GtkListBox`.

Testing Done:
Compile only.

Reviewed at https://reviews.imfreedom.org/r/650/
syntax: glob
.*.swp
.DS_Store
.flatpak-builder
*.pyc
*~
\#*\#
subprojects/*/
syntax: regexp
^build(.+)?\/
win32-install-dir(\.release)?
po\/pidgin\.pot$