compat: Remove non-Mac dependency on third_party/xnu

It looks like this was planned for future changes that haven't happened
yet. Current users of the .def files explicitly reference them, so
compat currently doesn't require this dependency.

Bug: fuchsia:66116
Change-Id: I99d0500188593b0de2210fe65e5794d1fe97a711
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/2640725
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>
GitOrigin-RevId: 2a777a4d4fb0d2c9e4c1f9fbf139ebcb545081ed
diff --git a/compat/BUILD.gn b/compat/BUILD.gn
index 54d9acb..4579ddf 100644
--- a/compat/BUILD.gn
+++ b/compat/BUILD.gn
@@ -165,10 +165,6 @@
 
   deps = [ "../util:no_cfi_icall" ]
 
-  if (!crashpad_is_mac) {
-    deps += [ "../third_party/xnu" ]
-  }
-
   if (crashpad_is_win) {
     deps += [ "../third_party/getopt" ]
   }