Remove unused and unimplemented abstract functions from GrRenderTarget

Remove unused and unimplemented abstract functions from GrRenderTarget

Remove unused and unimplemented abstract functions from GrRenderTarget.
The functions might cause confusion later.

BUG=skia:3388
Committed: https://skia.googlesource.com/skia/+/2340dcb02c683885707a24ed6ecd7732c29735dc

[Kimmo Kinnunen, 2015-02-03 12:57:54]

kkinnunen@nvidia.com changed reviewers:
+ bsalomon@google.com

[bsalomon, 2015-02-03 16:47:54]

lgtm

[bsalomon, 2015-02-03 16:55:18]

The CQ bit was checked by bsalomon@google.com

[commit-bot: I haz the power, 2015-02-03 16:56:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/865603007/1

[commit-bot: I haz the power, 2015-02-03 16:58:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-02-03 16:58:50]

Try jobs failed on following builders:
  Build-Ubuntu13.10-Clang-x86_64-Debug-Trybot on client.skia.compile
(http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu13.10-Cl...)

[Kimmo Kinnunen, 2015-02-04 06:13:43]

oops, forgot the part where they were trivially implemented, but not used. This
should not change the situation.

I take the liberty to still follow the lgtm and commit. If this is wrong, please
revert.

[Kimmo Kinnunen, 2015-02-04 06:13:47]

The CQ bit was checked by kkinnunen@nvidia.com

[commit-bot: I haz the power, 2015-02-04 06:14:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/865603007/20001

[commit-bot: I haz the power, 2015-02-04 06:20:23]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/2340dcb02c683885707a24ed6ecd7732c29735dc