Removed unused local variable

Copybara Import from #276

BEGIN_PUBLIC
Removed unused local variable (#276)

Closes #276
END_PUBLIC

COPYBARA_INTEGRATE_REVIEW=#276 from hauserx:unused_msvc_vars 72454ac
PiperOrigin-RevId: 697918518
Change-Id: I88fa8c6836d62cfcbc38818a4241fb623ebc7ae6

Author: hauserx

cc/private/toolchain/windows_cc_configure.bzl

@@ -649,7 +649,6 @@ def _get_msys_mingw_vars(repository_ctx):
 
 def _get_msvc_vars(repository_ctx, paths, target_arch = "x64", msvc_vars_x64 = None):
     """Get the variables we need to populate the MSVC toolchains."""
-    msvc_vars = dict()
     vc_path = find_vc_path(repository_ctx)
     missing_tools = None