The password is saved in an insecure way and is only used for
later auto-fill-in. Password managers are a better fit for that.

The proxy credentials are currently stored in an insecure way, and
should not be stored persistently if it can be avoided.

For architectural reasons, the credentials have to be saved for the
runtime of the program to be accessed by the network manager.

Clear the credentials at the end of the program.

These methods are no longer used due to insecure practices, thus
remove them.

They are no longer used anywhere.

No UBCryptoUtils object will ever created, so destroy() is a noop.
Remove unused public functions

They provide no public functions and as such can be safely removed.
Also remove them from the build system (qmake and cmake).

It hasn't worked for a few years due to API changes made by YT.

The dialog is inaccessible and uploading doesn't work due to outdated API

Youtube upload support gets removed, including this dialog

Publishing to YouTube was non-functional due to API changes on their part.
Since noone reported issues with it, it is reasonable to assume that there
are no users. Since the functionality is unmaintained, remove it entirely.

In previous commits, the upload function was made inaccessible. Now remove
the actual files.

The `youTubePublishingDialog.ui` form is unused since the
corresponding dialog code got removed.

Related settings like storing the username are removed.

Translations have to be cleaned up at a later point.