Remove implprefix arg to PluginManager #145
Description
As per discussion in #144 we plan to outright remove the implprefix kwarg to PluginManager after an appropriate PR has been made to pytest implementing the prefix based hook detection/registration.
Further discussion should be made here regarding a possible strategy pattern for hook detection outside of the regular explicit marking mechanism.
An initial thought is to instead offer prefix based registration through a prefix kwarg to PluginManager.register() if this is a feature we'd like to keep.