Revert "Added dead variable / code elimination to skslc."

This reverts commit 113628d76176a1ab3e6719c59efff23cd10ab213.

Reason for revert: Looks to have caused https://bugs.chromium.org/p/chromium/issues/detail?id=688939

Original change's description:
> Added dead variable / code elimination to skslc.
> 
> BUG=skia:
> 
> Change-Id: Ib037730803a8f222f099de0e001fe06ad452a22c
> Reviewed-on: https://skia-review.googlesource.com/7584
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> Reviewed-by: Ben Wagner <benjaminwagner@google.com>
> 

TBR=egdaniel@google.com,benjaminwagner@google.com,ethannicholas@google.com,reviews@skia.org
# Not skipping CQ checks because original CL landed > 1 day ago.
BUG=skia:

Change-Id: I85599e4ca2bc6bfd782edc163f67b64195d6ae65
Reviewed-on: https://skia-review.googlesource.com/8077
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/ir/SkSLFunctionDefinition.h b/src/sksl/ir/SkSLFunctionDefinition.h
index 7e7b115..bae8825 100644
--- a/src/sksl/ir/SkSLFunctionDefinition.h
+++ b/src/sksl/ir/SkSLFunctionDefinition.h
@@ -18,8 +18,8 @@
  * A function definition (a declaration plus an associated block of code).
  */
 struct FunctionDefinition : public ProgramElement {
-    FunctionDefinition(Position position, const FunctionDeclaration& declaration,
-                       std::unique_ptr<Statement> body)
+    FunctionDefinition(Position position, const FunctionDeclaration& declaration, 
+                       std::unique_ptr<Block> body)
     : INHERITED(position, kFunction_Kind)
     , fDeclaration(declaration)
     , fBody(std::move(body)) {}
@@ -29,7 +29,7 @@
     }
 
     const FunctionDeclaration& fDeclaration;
-    std::unique_ptr<Statement> fBody;
+    const std::unique_ptr<Block> fBody;
 
     typedef ProgramElement INHERITED;
 };