Revert "Relocate shaders to own dir"

This reverts commit fabe0b26d05624ce7374f6ca89bd66df6142534e.

Reason for revert: Last android roll failed with "external/skia/src/effects/SkGaussianEdgeShader.h:11:10: fatal error: 'SkShaderBase.h' file not found"

Original change's description:
> Relocate shaders to own dir
> 
> Consolidate all shader impls under src/shaders/.
> 
> Change-Id: I450e37541214704c1ad9e379d9d753b7cc62fac3
> Reviewed-on: https://skia-review.googlesource.com/17927
> Commit-Queue: Florin Malita <fmalita@chromium.org>
> Reviewed-by: Herb Derby <herb@google.com>
> 

TBR=mtklein@google.com,herb@google.com,fmalita@chromium.org,reed@google.com
No-Presubmit: true
No-Tree-Checks: true
No-Try: true

Change-Id: Idbb2b75053969df1dad9d8ce0217cd39189b9ddb
Reviewed-on: https://skia-review.googlesource.com/18020
Reviewed-by: Stan Iliev <stani@google.com>
Commit-Queue: Stan Iliev <stani@google.com>
45 files changed