Remove switch_services_to_plugin

[rjschwei]

At the end of 2024 it will be roughly 5 years since we switched the update server technology from SMT to RMT. During this switch we also switched from handing out http based URLs for the repositories to use the zypper url resolver mechanism. The switch_services_to_plugin code handles the transition from http based repo urls to resolver based urls. In order for this to be useful an instance would have to have been stopped for 5 years which means it is very unlikely that the user can get an updated cloud-regionsrv-client package from the update infrastructure to begin with.

Therefore the code can be removed. Removal after December 31st 2024.