Revert "Add Ganesh support for RGBA_16161616 and RG_half"

This reverts commit 156622513ffc385bb493eda8d4cf5cbed19350d1.

Reason for revert: valgrind

Original change's description:
> Add Ganesh support for RGBA_16161616 and RG_half
> 
> Change-Id: Ia424ff719c5fb8d1842a909ade09ad6f5f78f21f
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/219998
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

TBR=egdaniel@google.com,robertphillips@google.com

Change-Id: I7a8e99e70f575fb301ce289d9a04ebbec25b934b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/220739
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/gl/GrGLUtil.cpp b/src/gpu/gl/GrGLUtil.cpp
index b1f989c..f50932e 100644
--- a/src/gpu/gl/GrGLUtil.cpp
+++ b/src/gpu/gl/GrGLUtil.cpp
@@ -612,7 +612,6 @@
         case GR_GL_RGBA4:
         case GR_GL_RG8:
         case GR_GL_R16F:
-        case GR_GL_R16:
             return 2;
 
         case GR_GL_RGB8:
@@ -622,7 +621,6 @@
         case GR_GL_SRGB8_ALPHA8:
         case GR_GL_BGRA8:
         case GR_GL_RGB10_A2:
-        case GR_GL_RG16:
             return 4;
 
         case GR_GL_RGBA16F:
@@ -636,11 +634,11 @@
         case GR_GL_COMPRESSED_ETC1_RGB8:
             return 0;
 
-        // Experimental (for Y416 and mutant P016/P010)
-        case GR_GL_RG16F:
+        // Experimental (for P016 and P010)
+        case GR_GL_R16:
+            return 2;
+        case GR_GL_RG16:
             return 4;
-        case GR_GL_RGBA16:
-            return 8;
     }
 
     SK_ABORT("Invalid GL format");