Revert "Add Ganesh support for LUM16F"

This reverts commit 2f6c8af73a87d60e97ec2667a39cf597e1f463b2.

Reason for revert: Failing on some bots

Original change's description:
> Add Ganesh support for LUM16F
> 
> When Chrome has a LUM16F texture they tell Skia it is R16F. Although this has been working for them so far it causes trouble with some upcoming changes.
> 
> Change-Id: Ic2143ec69f33a17cb1cb64f6ebc39bffd94a5e68
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/228557
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

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

Change-Id: Ie52150f4f5255a2db697b9f0e810eff2042eadec
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/228560
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/sksl/SkSLGLSLCodeGenerator.cpp b/src/sksl/SkSLGLSLCodeGenerator.cpp
index 2f2989b..4ac8ed4 100644
--- a/src/sksl/SkSLGLSLCodeGenerator.cpp
+++ b/src/sksl/SkSLGLSLCodeGenerator.cpp
@@ -1143,19 +1143,18 @@
     switch (modifiers.fLayout.fFormat) {
         case Layout::Format::kUnspecified:
             break;
-        case Layout::Format::kRGBA32F:      // fall through
+        case Layout::Format::kRGBA32F: // fall through
         case Layout::Format::kR32F:
             this->write("highp ");
             break;
-        case Layout::Format::kRGBA16F:      // fall through
-        case Layout::Format::kR16F:         // fall through
-        case Layout::Format::kLUMINANCE16F: // fall through
+        case Layout::Format::kRGBA16F: // fall through
+        case Layout::Format::kR16F:    // fall through
         case Layout::Format::kRG16F:
             this->write("mediump ");
             break;
-        case Layout::Format::kRGBA8:        // fall through
-        case Layout::Format::kR8:           // fall through
-        case Layout::Format::kRGBA8I:       // fall through
+        case Layout::Format::kRGBA8:  // fall through
+        case Layout::Format::kR8:     // fall through
+        case Layout::Format::kRGBA8I: // fall through
         case Layout::Format::kR8I:
             this->write("lowp ");
             break;