Do not run gyp as gclient hook for building for node.

This causes issues when running tools/node/fetch_deps.py on systems without
gyp as pre-installed python module. And we do not even need to do this for
building for node (with GN).

R=machenbach@chromium.org

Bug: v8:6105
Change-Id: If0089dedf176bb509b9fd000e5fe829f8a32bac6
Reviewed-on: https://chromium-review.googlesource.com/852458Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50416}

DEPS

@@ -319,6 +319,7 @@ hooks = [
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     'name': 'regyp_if_needed',
     'pattern': '.',
+    'condition': 'build_for_node != True',
     'action': ['python', 'v8/gypfiles/gyp_v8', '--running-as-hook'],
   },
   # Download and initialize "vpython" VirtualEnv environment packages.