Revert of Add config options to run different GPU APIs to dm and nanobench (patchset...

Revert of Add config options to run different GPU APIs to dm and nanobench (patchset #18 id:340001 of https://codereview.chromium.org/1490113005/ )

Reason for revert:
This CL changed 1200 images on gold, when I wouldn't expect any diffs from the description.

Original issue's description:
> Add config options to run different GPU APIs to dm and nanobench
>
> Add extended config specification form that can be used to run different
> gpu backend with different APIs.
>
> The configs can be specified with the form:
> gpu(api=string,dit=bool,nvpr=bool,samples=int)
>
> This replaces and removes the --gpuAPI flag.
>
> All existing configs should still work.
>
> Adds following documentation:
>
> out/Debug/dm --help config
>
> Flags:
>     --config:	type: string	default: 565 8888 gpu nonrendering
>         Options: 565 8888 debug gpu gpudebug gpudft gpunull msaa16 msaa4
>         nonrendering null nullgpu nvprmsaa16 nvprmsaa4 pdf pdf_poppler skp svg
>         xps or use extended form 'backend(option=value,...)'.
>
>         Extended form: 'backend(option=value,...)'
>
>         Possible backends and options:
>
>         gpu(api=string,dit=bool,nvpr=bool,samples=int)	GPU backend
>         	api	type: string	default: native.
>         	    Select graphics API to use with gpu backend.
>         	    Options:
>         		native			Use platform default OpenGL or OpenGL ES backend.
>         		gl    			Use OpenGL.
>         		gles  			Use OpenGL ES.
>         		debug 			Use debug OpenGL.
>         		null  			Use null OpenGL.
>         	dit	type: bool	default: false.
>         	    Use device independent text.
>         	nvpr	type: bool	default: false.
>         	    Use NV_path_rendering OpenGL and OpenGL ES extension.
>         	samples	type: int	default: 0.
>         	    Use multisampling with N samples.
>
>         Predefined configs:
>
>         	gpu      	= gpu()
>         	msaa4    	= gpu(samples=4)
>         	msaa16   	= gpu(samples=16)
>         	nvprmsaa4	= gpu(nvpr=true,samples=4)
>         	nvprmsaa16	= gpu(nvpr=true,samples=16)
>         	gpudft    	= gpu(dit=true)
>         	gpudebug  	= gpu(api=debug)
>         	gpunull   	= gpu(api=null)
>         	debug     	= gpu(api=debug)
>         	nullgpu   	= gpu(api=null)
>
> BUG=skia:2992
>
> Committed: https://skia.googlesource.com/skia/+/e13ca329fca4c28cf4e078561f591ab27b743d23
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1490113005
>
> Committed: https://skia.googlesource.com/skia/+/c8b4336444e7b90382e04e33665fb3b8490b825b

TBR=mtklein@google.com,bsalomon@google.com,scroggo@google.com,kkinnunen@nvidia.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:2992

Review URL: https://codereview.chromium.org/1536963002