Drop api version suffix from library name

Also please see https://github.com/PipeWire/pipewire/issues/77. If we keep using api version as suffix for library name, everyone will have to search for libpipewire-0.1 for old PW, then libpipewire-0.2 for current PW and in future for libpipewire-0.3 and so on, which is not good and makes supporting multiple PW versions complicated.