Keep kwalletmanager5 name for now

Instead of doing a partial transition to the new name that breaks in various places, let's keep the current name and plan for a "full" transition / rename at a later time.

See:

• https://github.com/flathub/org.kde.kwalletmanager5/pull/24
• https://github.com/flathub/org.kde.kwalletmanager5/pull/26

See:

• !44 (merged)
• !45 (merged)
• !50 (merged)

See: https://bugs.kde.org/show_bug.cgi?id=489916