Remove unused and useless variables. Also fix the build when
SWIFTSHADER_ENABLE_VULKAN_DEBUGGER is enabled.

Bug: b/145758253
Change-Id: Ie49dd88d6716b24fe31baa8f8d162e7dacfa5a3c
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/43268Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>