Revert of Turned on SkSL->GLSL compiler

src/sksl/README

-Overview
-========
-
-SkSL ("Skia Shading Language") is a variant of GLSL which is used as Skia's 
-internal shading language. SkSL is, at its heart, a single standardized version
-of GLSL which avoids all of the various version and dialect differences found
-in GLSL "in the wild", but it does bring a few of its own changes to the table.
-
-Skia uses the SkSL compiler to convert SkSL code to GLSL, GLSL ES, or SPIR-V
-before handing it over to the graphics driver.
-
-Differences from GLSL
-=====================
-
-SkSL is based on GLSL 4.5. For the most part, write SkSL exactly as you would
-desktop GLSL, and the SkSL compiler will take care of version and dialect
-differences (for instance, you always use "in" and "out", and skslc will handle
-translating them to "varying" and "attribute" as appropriate). Be aware of the 
-following differences between SkSL and GLSL:
-
-* no #version or "precision" statement is required, and they will be ignored if
-  present
-* the output color is sk_FragColor (do not declare it)
-* lowp, mediump, and highp are always permitted (but will only be respected if 
-  you run on a GLES device)
-* you do not need to include ".0" to make a number a float (meaning that
-  "vec2(x, y) * 4" is perfectly legal in SkSL, unlike GLSL where it would have
-  to be expressed "vec2(x, y) * 4.0". There is no performance penalty for this, 
-  as the number is converted to a float at compile time)
-* some built-in functions and one or two rarely-used language features are not
-  yet supported (sorry!)
-
-SkSL is still under development, and is expected to diverge further from GLSL
-over time.