Remove unneeded GN import.

Bug: None
Change-Id: Iebc51f84019f505c09fae9f40dc5f92c99fe3c7b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/177247
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31532}

rtc_base/synchronization/BUILD.gn

diff --git a/rtc_base/synchronization/BUILD.gn b/rtc_base/synchronization/BUILD.gn
index 6bc6447..f6e6d0b 100644
--- a/rtc_base/synchronization/BUILD.gn
+++ b/rtc_base/synchronization/BUILD.gn
@@ -11,7 +11,6 @@
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
-import("//third_party/google_benchmark/buildconfig.gni")
 
 rtc_library("yield") {
   sources = [