ci: bluetooth-tests: Remove stale clang-related variables

This commit removes stale clang-related variables that are not used by
the bluetooth-tests workflow.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

.github/workflows/bluetooth-tests.yaml

@@ -28,7 +28,6 @@ jobs:
     env:
       ZEPHYR_TOOLCHAIN_VARIANT: zephyr
       ZEPHYR_SDK_INSTALL_DIR: /opt/toolchains/zephyr-sdk-0.15.0
-      CLANG_ROOT_DIR: /usr/lib/llvm-12
       BSIM_OUT_PATH: /opt/bsim/
       BSIM_COMPONENTS_PATH: /opt/bsim/components
       EDTT_PATH: ../tools/edtt