Clean up ifdefs in SkGifCodec

Clean up ifdefs in SkGifCodec

Since codec uses the same version of giflib everywhere,
I believe these are unnecessary.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/b30e9d3960567571946ed89cbe7f5a2bd8255f85

[msarett, 2015-08-21 13:24:26]

msarett@google.com changed reviewers:
+ djsollen@google.com, scroggo@google.com

[msarett, 2015-08-21 13:24:26]

https://codereview.chromium.org/1309763002/diff/1/src/codec/SkCodec_libgif.cpp
File src/codec/SkCodec_libgif.cpp (right):

https://codereview.chromium.org/1309763002/diff/1/src/codec/SkCodec_libgif.cp...
src/codec/SkCodec_libgif.cpp:70: #if GIFLIB_MAJOR < 5 || (GIFLIB_MAJOR == 5 &&
GIFLIB_MINOR == 0)
This is the only one I haven't removed.  I think we should keep it in until we
finish the upgrade from 5.0.4 to 5.1.1.

[djsollen, 2015-08-21 13:51:51]

lgtm

[msarett, 2015-08-21 13:52:23]

The CQ bit was checked by msarett@google.com

[commit-bot: I haz the power, 2015-08-21 13:52:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1309763002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1309763002/1

[commit-bot: I haz the power, 2015-08-21 13:58:46]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/b30e9d3960567571946ed89cbe7f5a2bd8255f85

[scroggo, 2015-08-26 16:52:49]

FWIW, any time *we* build SkGifCodec, we'll use a particular version of giflib,
but in theory, some external project could build Skia using a different version
(or even just use the version installed on their local machine). I do not know
whether it makes sense to support that use case. (And the code is definitely
cleaner this way!)