[extensions] copy eu-strip in buildtools

This is for strange error in
https://ci.chromium.org/p/chromium/builders/ci/Deterministic%20Linux/24185

Change-Id: Ief72e01492d5f2567985cb66857763bc955cd4ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1714947
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680336}

extensions/shell/installer/linux/BUILD.gn

@@ -62,7 +62,7 @@ action("strip_app_shell_binary") {
 copy("common_packaging_files") {
   visibility = [ ":*" ]
   sources = [
-    "/usr/bin/eu-strip",
+    "//buildtools/third_party/eu-strip/bin/eu-strip",
     "common/installer.include",
     "common/wrapper",
   ]