Fix "list comprehension redefines 'x'" warnings from pyflakes

  $ git ls-files | grep py$ | xargs pyflakes
  subcmds/stage.py:101: list comprehension redefines 'p' from line 63
  subcmds/sync.py:784: list comprehension redefines 'p' from line 664
  subcmds/upload.py:467: list comprehension redefines 'avail' from line 454

Change-Id: Ia65d1a72ed185ab3357e1a91ed4450c719e75a7c
diff --git a/subcmds/upload.py b/subcmds/upload.py
index 38c061d..fa80c3d 100644
--- a/subcmds/upload.py
+++ b/subcmds/upload.py
@@ -464,8 +464,8 @@
                       self.manifest.topdir,
                       self.manifest.manifestProject.GetRemote('origin').url,
                       abort_if_user_denies=True)
-      pending_proj_names = [project.name for (project, avail) in pending]
-      pending_worktrees = [project.worktree for (project, avail) in pending]
+      pending_proj_names = [project.name for (project, available) in pending]
+      pending_worktrees = [project.worktree for (project, available) in pending]
       try:
         hook.Run(opt.allow_all_hooks, project_list=pending_proj_names,
                  worktree_list=pending_worktrees)