Remove definition and usage of macro GTEST_RELATIVE_PATH.

The macro GTEST_RELATIVE_PATH is obsolete and since it is always
defined this CL just removes it.

Bug: webrtc:9564
Change-Id: Ieafa5b77351c4df87864588ba6b3de8f60d54e89
Reviewed-on: https://webrtc-review.googlesource.com/92080
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24226}
diff --git a/BUILD.gn b/BUILD.gn
index cba086c..2e3c91a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -104,12 +104,7 @@
     defines += [ "WEBRTC_NON_STATIC_TRACE_EVENT_HANDLERS=0" ]
   }
   if (build_with_chromium) {
-    defines += [
-      # TODO(kjellander): Cleanup unused ones and move defines closer to
-      # the source when webrtc:4256 is completed.
-      "GTEST_RELATIVE_PATH",
-      "WEBRTC_CHROMIUM_BUILD",
-    ]
+    defines += [ "WEBRTC_CHROMIUM_BUILD" ]
     include_dirs = [
       # The overrides must be included first as that is the mechanism for
       # selecting the override headers in Chromium.