Revert of Turned on SkSL->GLSL compiler (patchset #41 id:880001 of https://codereview.chromium.org/2288033003/ )

Reason for revert:
1) Chromium roll failures: https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/307297/steps/screenshot_sync_tests%20on%20NVIDIA%20GPU%20on%20Linux%20%28with%20patch%29%20on%20Linux/logs/stdio

2) G3 roll failures

3) iOS failures: https://uberchromegw.corp.google.com/i/client.skia/builders/Perf-iOS-Clang-iPad4-GPU-SGX554-Arm7-Release/builds/7177/steps/perf_skia%20on%20iOS-9.2/logs/stdio

Original issue's description:
> Turned on SkSL->GLSL compiler
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2288033003
>
> Committed: https://skia.googlesource.com/skia/+/9b0fe3d125f237d9884732a48414fa85fc71b4e3
> Committed: https://skia.googlesource.com/skia/+/b12b3c6908c62c908b3680be01e3b5bfd30de310
> Committed: https://skia.googlesource.com/skia/+/f008b0a59f45c0d4bea3e66faf3b01805009ec89

TBR=benjaminwagner@google.com,bsalomon@google.com,egdaniel@google.com,ethannicholas@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.chromium.org/2387643003
diff --git a/src/sksl/SkSLParser.h b/src/sksl/SkSLParser.h
index d1ae0d0..75f304b 100644
--- a/src/sksl/SkSLParser.h
+++ b/src/sksl/SkSLParser.h
@@ -35,7 +35,6 @@
 struct ASTLayout;
 struct ASTModifiers;
 struct ASTParameter;
-struct ASTPrecision;
 struct ASTReturnStatement;
 struct ASTStatement;
 struct ASTSuffix;
@@ -101,7 +100,7 @@
     // don't need to call any of these outside of the parser. The function declarations in the .cpp
     // file have comments describing the grammar rules.
 
-    std::unique_ptr<ASTDeclaration> precision();
+    void precision();
 
     std::unique_ptr<ASTDeclaration> directive();