Revert "Add Gray8 pixel config"

This reverts commit f2956459f707de596dcb2c79a7ee1fa62d599c0d.

Reason for revert: GM and image failures on some bots (rendering red, not gray).

Original change's description:
> Add Gray8 pixel config
> 
> This is still just linear (non-sRGB), but adding sRGB will
> be the next step. I've verified that this is really making
> R8 textures when uploading Gray8 bitmaps. Tests pass, and
> the all_bitmap_configs GM still renders correctly (unlike
> when we just mapped Gray8 to Alpha8).
> 
> This adds another pixel config, which could grow our cache
> footprint, but the benefits of not using 4bpp for 1bpp data
> should outweigh that?
> 
> BUG=skia:6110
> 
> Change-Id: I4fc4c2479fc25f1d278e174a9bb5b542a0cb184c
> Reviewed-on: https://skia-review.googlesource.com/6817
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>
> 

TBR=bsalomon@google.com,robertphillips@google.com,brianosman@google.com,reviews@skia.org
BUG=skia:6110
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I95a4fc0450a569d5791f6bceb7fae61c7e5eba61
Reviewed-on: https://skia-review.googlesource.com/6838
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index fd8aba0..30f596f 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -680,7 +680,6 @@
     static const GrPixelConfig kFallback[] = {
         kUnknown_GrPixelConfig,        // kUnknown_GrPixelConfig
         kRGBA_8888_GrPixelConfig,      // kAlpha_8_GrPixelConfig
-        kUnknown_GrPixelConfig,        // kGray_8_GrPixelConfig
         kUnknown_GrPixelConfig,        // kIndex_8_GrPixelConfig
         kRGBA_8888_GrPixelConfig,      // kRGB_565_GrPixelConfig
         kRGBA_8888_GrPixelConfig,      // kRGBA_4444_GrPixelConfig
@@ -701,22 +700,21 @@
 
     GR_STATIC_ASSERT(0  == kUnknown_GrPixelConfig);
     GR_STATIC_ASSERT(1  == kAlpha_8_GrPixelConfig);
-    GR_STATIC_ASSERT(2  == kGray_8_GrPixelConfig);
-    GR_STATIC_ASSERT(3  == kIndex_8_GrPixelConfig);
-    GR_STATIC_ASSERT(4  == kRGB_565_GrPixelConfig);
-    GR_STATIC_ASSERT(5  == kRGBA_4444_GrPixelConfig);
-    GR_STATIC_ASSERT(6  == kRGBA_8888_GrPixelConfig);
-    GR_STATIC_ASSERT(7  == kBGRA_8888_GrPixelConfig);
-    GR_STATIC_ASSERT(8  == kSRGBA_8888_GrPixelConfig);
-    GR_STATIC_ASSERT(9  == kSBGRA_8888_GrPixelConfig);
-    GR_STATIC_ASSERT(10 == kRGBA_8888_sint_GrPixelConfig);
-    GR_STATIC_ASSERT(11 == kETC1_GrPixelConfig);
-    GR_STATIC_ASSERT(12 == kLATC_GrPixelConfig);
-    GR_STATIC_ASSERT(13 == kR11_EAC_GrPixelConfig);
-    GR_STATIC_ASSERT(14 == kASTC_12x12_GrPixelConfig);
-    GR_STATIC_ASSERT(15 == kRGBA_float_GrPixelConfig);
-    GR_STATIC_ASSERT(16 == kAlpha_half_GrPixelConfig);
-    GR_STATIC_ASSERT(17 == kRGBA_half_GrPixelConfig);
+    GR_STATIC_ASSERT(2  == kIndex_8_GrPixelConfig);
+    GR_STATIC_ASSERT(3  == kRGB_565_GrPixelConfig);
+    GR_STATIC_ASSERT(4  == kRGBA_4444_GrPixelConfig);
+    GR_STATIC_ASSERT(5  == kRGBA_8888_GrPixelConfig);
+    GR_STATIC_ASSERT(6  == kBGRA_8888_GrPixelConfig);
+    GR_STATIC_ASSERT(7  == kSRGBA_8888_GrPixelConfig);
+    GR_STATIC_ASSERT(8  == kSBGRA_8888_GrPixelConfig);
+    GR_STATIC_ASSERT(9  == kRGBA_8888_sint_GrPixelConfig);
+    GR_STATIC_ASSERT(10 == kETC1_GrPixelConfig);
+    GR_STATIC_ASSERT(11 == kLATC_GrPixelConfig);
+    GR_STATIC_ASSERT(12 == kR11_EAC_GrPixelConfig);
+    GR_STATIC_ASSERT(13 == kASTC_12x12_GrPixelConfig);
+    GR_STATIC_ASSERT(14 == kRGBA_float_GrPixelConfig);
+    GR_STATIC_ASSERT(15 == kAlpha_half_GrPixelConfig);
+    GR_STATIC_ASSERT(16 == kRGBA_half_GrPixelConfig);
     GR_STATIC_ASSERT(SK_ARRAY_COUNT(kFallback) == kGrPixelConfigCnt);
 }