Revert "Update GN prebuilt"

This patch broke the build.

This reverts commit 7bd05f2bd14a0d0ac2b0b5eff1b098bbff1440db.

Change-Id: I15649d060ddd13c8cba94f4da101939521fd0363
diff --git a/linux64/gn.sha1 b/linux64/gn.sha1
index 99fe0b0..af4f6ef 100644
--- a/linux64/gn.sha1
+++ b/linux64/gn.sha1
@@ -1 +1 @@
-73a17cc71987e233d12b16e4f058f55cc164675e
+2d0a1468089dfda652090b5b43f44787be137475
diff --git a/mac/gn.sha1 b/mac/gn.sha1
index cd89fd4..5d89d36 100644
--- a/mac/gn.sha1
+++ b/mac/gn.sha1
@@ -1 +1 @@
-78fa88a52c89aeef92e016b5cf0b7458642591df
+256d6d6497d83c662100c4d2e22f849ad7e7bd99