Remove SkImageDecoder_libjpeg and all references to it

Per Elliot's investigations, we have never built SkImageDecoder_libjpeg since we started building with gyp.
Asking Brian to review since that original gyp commit was his - why did we explicitly exclude the libjpeg decoder on every platform?

Resolve http://code.google.com/p/skia/issues/detail?id=52 by removing dead code from the library.

[bsalomon, 2012-03-02 15:10:18]

I'm sure I just copied that from chromium's skia.gyp which must use its own jpeg
decoder.

Adding Mike because I'm not sure if the src file has value or not.

[TomH, 2012-03-02 15:13:53]

On 2012/03/02 15:10:18, bsalomon wrote:
> Adding Mike because I'm not sure if the src file has value or not.

There was already an email discussion with Mike, Elliot, Derek - not used in
Android.

[epoger, 2012-03-02 15:14:19]

LGTM

I didn't know about http://code.google.com/p/skia/issues/detail?id=52 ('Add
casting to char to avoid compiler warnings') ... I guess we used to build that
file, before we moved to gyp.

I think it's fine to go ahead and remove it.  We'll find out soon enough if
there is some mysterious dependency on it.

[bsalomon, 2012-03-02 15:18:40]

On 2012/03/02 15:14:19, epoger wrote:
> LGTM
> 
> I didn't know about http://code.google.com/p/skia/issues/detail?id=52 ('Add
> casting to char to avoid compiler warnings') ... I guess we used to build that
> file, before we moved to gyp.
> 
> I think it's fine to go ahead and remove it.  We'll find out soon enough if
> there is some mysterious dependency on it.

LGTM

[TomH, 2012-03-02 15:38:38]

Closed with r3302.