Remove the 'removed' condition_variable field. It is not used.

Don't bother copying and unlocking before returning a field - this is not required.

Bug: b/133127573
Change-Id: Ic8e29e6b6008e16b6abd043ccfa9014e203ce69a
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31678
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <headlessclayton@gmail.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>