Remove thread refcount and remove NaClAppDtor()

Remove thread refcount and remove NaClAppDtor()

Following r2358, where support for signal stacks was added,
NaClAppThreadDtor() must now be called from the thread that is
shutting down, or the signal stack will be unregistered for the wrong
thread.

This means the refcount for threads should be removed, to ensure that
it is not used unsafely, so remove NaClAppThreadIncRef() (which was
not used anyway) and remove NaClAppThreadDecRef().

NaClAppDtor() called NaClAppThreadDecRef() but is basically unused,
because it is not able to shut down running threads safely.  There is
a TODO for its removal, so remove it.

This leaves other code unused, so remove it too:

 * NaClAppFreeAllMemory()
 * NaClAppFreeWalker()
 * NaClTeardownMprotectGuards()
 * guard_pages_initialized field

web_worker_stub.c called NaClAppDtor() but is dead code.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=560
TEST=existing tests

Committed: http://code.google.com/p/nativeclient/source/detail?r=2458

[Mark Seaborn, 2010-06-04 14:54:12]

I could split this up into a couple of commits, but the review process/tools
seem to favour doing it in one go.

I'd be inclined to remove web_worker_stub.c, since it's dead code.  What do you
think?

[Cliff L. Biffle, 2010-06-08 00:14:24]

LGTM.  Woooooooooooooooooo!

http://codereview.chromium.org/2659002/diff/2001/3013
File src/native_client/src/trusted/service_runtime/sel_ldr_test.cc (left):

http://codereview.chromium.org/2659002/diff/2001/3013#oldcode83
src/native_client/src/trusted/service_runtime/sel_ldr_test.cc:83:
NaClAppDtor(&app);
Hm, tests are actually the one context where I'd expect the Dtor to be useful! 
Does this test still pass?

[Mark Seaborn, 2010-06-08 17:50:43]

On 2010/06/08 00:14:24, Cliff L. Biffle wrote:
> LGTM.  Woooooooooooooooooo!
> 
> http://codereview.chromium.org/2659002/diff/2001/3013
> File src/native_client/src/trusted/service_runtime/sel_ldr_test.cc (left):
> 
> http://codereview.chromium.org/2659002/diff/2001/3013#oldcode83
> src/native_client/src/trusted/service_runtime/sel_ldr_test.cc:83:
> NaClAppDtor(&app);

> Hm, tests are actually the one context where I'd expect the Dtor to
> be useful!  Does this test still pass?

Yep, it still passes.  I guess it's just leaking a small amount of
space between test cases, which I think is fine for a test.

Thanks,
Mark