BUILD.gn: Remove XCB sources for chromeos.

VK_USE_PLATFORM_XCB_KHR is no longer defined for chromeos.

Bug: b/209030951
Change-Id: Iad28747fb06e13126ea83e1a38b15293a945bcbb
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/61550
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Result: Ben Clayton <bclayton@google.com>
diff --git a/src/WSI/BUILD.gn b/src/WSI/BUILD.gn
index 3357650..42239fb 100644
--- a/src/WSI/BUILD.gn
+++ b/src/WSI/BUILD.gn
@@ -33,7 +33,7 @@
     "VkSwapchainKHR.hpp",
   ]
 
-  if (is_linux || is_chromeos) {
+  if (is_linux) {
     sources += [
       "XcbSurfaceKHR.cpp",
       "XcbSurfaceKHR.hpp",