Remove deprecated auth sources

[techknowlogick]

Entra ID users should use the OIDC oauth2 provider.

They will still be shown if the instance has a previous Azure AD source configured.

[lunny]

I mean

existAuthSources := getExistingAzureADAuthSources(ctx)
for _, provider := range gothProviders {
		if isAzureProvider(provider.Name()) && !slices.Contains(existAuthSources, provider.Name()) {
			continue
		}