Remove CL env variable in Windows MSVC workflow

Change-Id: Ifc36f69b96b67bd4cc88ea964291debf33ccb098

.github/workflows/windows.yml

diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index 99b82e3..9fe8b28 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -83,7 +83,6 @@
         shell: powershell
     env:
       CCACHE_DIR: ${{github.workspace}}/ccache
-      CL: /MP
       CMAKE_GENERATOR: ${{matrix.generator}}
       CMAKE_GENERATOR_PLATFORM: ${{matrix.arch}}
     strategy: