mojom: Remove braces from module statements and make them come first.

So, instead of:

import "bar.mojom";
module foo {
  ...
}

You'll do:

module foo;
import "bar.mojom";
...

(Note that the grammar in the parser doesn't capture the ordering
constraint. It's hard to do so while keeping the grammar LR(1) AFAICT.
So instead we enforce the ordering "manually".)

Also delete mojo/spy/PRESUBMIT.py since it's broken. We'll delete
mojo/spy separately.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/687793004