Revert of Update feSpotLight to match spec (patchset #2 id:20001 of https://coderevie...

Revert of Update feSpotLight to match spec (patchset #2 id:20001 of https://codereview.chromium.org/1403403003/ )

Reason for revert:
re-land once layout test have been disabled (so they can be rebased)

Original issue's description:
> Update feSpotLight to match spec
>
> This change updates feSpotLight to match the spec via two changes:
>
> 1) specularExponent is ignored if the spotlight has no coneAngle (GPU
>    bug only). This change updates the GPU path so that it matches the
>    CPU path and the spec in this regard.
>
> 2) specularExponent is clamped to the 1-128 range. The spec does not
>    specify a clamp for the specularExponent attribute of feSpotLight.
>    Note that the spec *does* specify this clamp for the
>    specularExponent attribute of feSpecularLighting. It looks like we
>    incorrectly applied this to both specularExponent attributes.
>
>    This change (along with a parallel change in Blink) allows us to pass
>    the SVG filter effects conformance test here:
>    http://www.w3.org/Graphics/SVG/Test/20110816/harness/htmlObject/filters-light-01-f.html
>
>    Additionally, this brings our behavior in line with Safari and Edge’s
>    behavior on this filter.
>
> Two new cases were added to gm/lighting.cpp to catch these issues:
> - The existing spotlight case exercised the path where our specular
>   exponent was between 1-128 and had a limiting cone angle.
> - The first new spotlight case exercises the path where our specular
>   exponent is between 1-128 and we do not have a limiting cone angle.
> - The second new spotlight case exercises the path where the specular
>   exponent is not within the 1-128 range, to ensure that we don’t
>   incorrectly clip to this range.
>
> BUG=472849
>
> Committed: https://skia.googlesource.com/skia/+/c84ccb070258db2803a9e8f532bfe7239a737063

TBR=senorblanco@google.com,senorblanco@chromium.org,bsalomon@google.com,ericrk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=472849

Review URL: https://codereview.chromium.org/1417463006