Disable vaapi and rust features by default + cleanup unused variable
commit c67034c5:
Remove unused variable in meson.build
We don't use this anywhere. It's confusing.
commit 7f231c2d:
Disable rust feature option by default
The only requirement for the rust plugins is that a rust toolchain be
present on the system. This is problematic:
1. This means gst-build on Windows is broken by default if you have
a Rust toolchain, since glib can't be used uninstalled
2. No output is printed on Windows at all while the rust plugins are
being built. `custom_target()`'s `console:` keyword argument seems
to be broken on some Windows shells.
3. Even on Linux/macOS having this enabled by default is problematic
since it more than doubles the total build time.
4. The biggest issue with having it enabled by default is that it does
not dependency tracking, so we always run `cargo`, which might
update crates. This increases friction when you're working on
unrelated code.
commit 6dfcecb1:
Disable vaapi feature by default
Having vaapi decoders/encoders accidentally available by default often
causes strange test failures or weird behaviour since the plugins are
sometimes buggy or have different behaviour.