Revert of added constant folding & branch elimination to skslc (patchset #3 id:40001...

Revert of added constant folding & branch elimination to skslc (patchset #3 id:40001 of https://codereview.chromium.org/2489673002/ )

Reason for revert:
Breaking the DEPS roll:

../../third_party/skia/src/sksl/SkSLIRGenerator.cpp:257:70: error: chosen constructor is explicit in copy-initialization
            return std::unique_ptr<Statement>(new Block(s.fPosition, { }, fSymbolTable));
                                                                     ^~~
../../build/linux/debian_wheezy_amd64-sysroot/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/debug/vector:77:7: note: constructor declared here
      vector(const _Allocator& __a = _Allocator())
      ^
../../third_party/skia/src/sksl/ir/SkSLBlock.h:20:70: note: passing argument to parameter 'statements' here
    Block(Position position, std::vector<std::unique_ptr<Statement>> statements,
                                                                     ^

Original issue's description:
> added constant folding & branch elimination to skslc
>
> BUG=skia:
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2489673002
>
> Committed: https://skia.googlesource.com/skia/+/6136310ee8f43247548bcefcaeca6d43023c10aa

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

Review-Url: https://codereview.chromium.org/2494523002