VST3 Client: Avoid calling performEdit during setState

The host is guaranteed to re-scan all parameter values after setting a
new state on the plugin, so there's no need to notify the host about
parameter changes that happen during the setState call.

This also avoids a problem where Bitwig would complain about invalid
parameter IDs in 'engine.log' when loading projects containing JUCE
VST3s. These log messages were produced because a call to setState was
made before Bitwig registered the plugin's parameters, and the setState
call in turn called performEdit with parameter IDs that were yet to be
registered.