Fix seed_steps for generator annotation recipes.

scripts/slave/recipes_test/run_presubmit.chromium.expected

 [
   {
    "cmd": ["[DEPOT_TOOLS_ROOT]/gclient", "config", "--spec", "solutions = [{'managed': True, 'custom_vars': {'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk', 'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'http://src.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s'}, 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src', 'custom_deps': {'src/third_party/WebKit/LayoutTests': None, 'src/webkit/data/layout_tests/LayoutTests': None}, 'deps_file': 'DEPS', 'safesync_url': '', 'name': 'src'}]\n"],
    "name": "gclient setup",
    "seed_steps": ["gclient setup", "gclient clean", "gclient sync"]
   },
   {
    "cmd": ["[DEPOT_TOOLS_ROOT]/gclient", "revert", "--nohooks"],
-   "name": "gclient clean"
+   "name": "gclient clean",
+   "seed_steps": []
   },
   {
    "cmd": ["[DEPOT_TOOLS_ROOT]/gclient", "sync", "--nohooks"],
-   "name": "gclient sync"
+   "name": "gclient sync",
+   "seed_steps": []
   },
   {
    "cmd": ["[DEPOT_TOOLS_ROOT]/apply_issue", "-r", "[SLAVE_BUILD_ROOT]/src/", "-i", 12853011, "-p", 1, "-s", "https://chromiumcodereview.appspot.com", "-e", "commit-bot@chromium.org"],
    "name": "apply_issue"
   },
   {
    "cmd": ["[DEPOT_TOOLS_ROOT]/presubmit_support.py", "--root", "[SLAVE_BUILD_ROOT]/src/", "--commit", "--verbose", "--verbose", "--issue", 12853011, "--patchset", 1, "--skip_canned", "CheckRietveldTryJobExecution", "--skip_canned", "CheckTreeIsOpen", "--skip_canned", "CheckBuildbotPendingBuilds", "--rietveld_url", "https://chromiumcodereview.appspot.com", "--rietveld_email", "", "--rietveld_fetch"],
    "name": "presubmit"
   }
 ]