Clean up generate_event_interfaces.py

Clean up generate_event_interfaces.py

Follow-up to the split CL.
Just clean-up, no changes to generated EventInterfaces.in.

* Rename to generate_event_interfaces (from "*_names")
This is b/c:
- the output file is called EventInterfaces.in
- the output file is used for both EventFactory and EventNames

* Remove EventInterfaces.in from run-bindings-tests
This file is useless, and adds unnecessary complexity to r-b-t.
The actual output file is trivial:
namespace="Event"

Source/bindings/tests/idls/TestInterfaceEventConstructor
...and I've never looked at it during CG changes.

With it, we need to have 2 passes of compute_interfaces_info,
and a separate temporary file.
Without it, once Terry's CL lands, we'll have no individual files,
and we can just use one temporary directory, removing lots of
temp file complexity.

* Compute source_dir robustly (not using getcwd)

* Refactoring and renaming

Follow-up to:
Split generate_event_interfaces.py from compute_interfaces_info.py
https://codereview.chromium.org/185303008/

BUG=341748
R=haraken

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168599

[Nils Barth (inactive), 2014-03-04 07:12:38]

Follow-up clean-up.

[haraken, 2014-03-04 08:37:59]

LGTM

[Nils Barth (inactive), 2014-03-06 01:01:45]

The CQ bit was checked by nbarth@chromium.org

[commit-bot: I haz the power, 2014-03-06 01:01:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/nbarth@chromium.org/186433003/1

[commit-bot: I haz the power, 2014-03-06 08:18:30]

Change committed as 168599