Erase the "pending" directory after an update has been successfully installed

[Arcitec]

Electron-Updater does not clean up the pending directory after installing updates.

• Noticed in project: https://github.com/Vencord/Vesktop/blob/main/package.json
• Ticket: [Feature Request] Open Build Service Repos for Popular Distros (Fedora, Ubuntu, openSUSE, etc) Vencord/Vesktop#848 (comment)

Electron-Updater downloads the new package to ~/.cache/vesktop-updater/pending/vesktop-1.5.4.x86_64.rpm and installs it.

Then, the ~/.cache/vesktop-updater/pending directory remains on disk afterwards, wasting space forever, for no good reason.

This problem seemingly affects every platform because I saw the same issue on Windows mentioned here: #8073

Please consider erasing the pending directory after installing updates. It saves disk space. A simple algorithm for this would literally just be "if the update check doesn't find any updates, erase pending dir on disk since there's nothing new to fetch".