Don't copy any VST3 state preamble

Bitwig prepends some data when passing an `IBStream*` to the plugin, and
when we do copy it iZotope Rx7 plugins cannot load their state (even if
we also copy over the same seek position). Not copying that preamble
fixes the issue, and it seems like it doesn't break anything.

CHANGELOG.md

@@ -105,6 +105,7 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 - Fixed another potential freezing issue in **REAPER** that could happen when the
   when the plugin resizes itself while sending a parameter change to the host,
   if REAPER's 'disable saving full plug-in state' is not disabled.
+- Fixed saving and loading _iZotope Rx7_ plugin state in **Bitwig Studio**.
 - Fixed a potential assertion failure when setting VST3 preset data. This would
   depend on the `libstdc++` version used to built yabridge with.
 - _PSPaudioware InifniStrip_ would fail to initialize because the plugin expects