This reverts commit 1dc0d394.

Reason for revert: Causes a failure on the bots. See: http://anglebug.com/5206

Original change's description:
> Allow rendering to half float in ES2 contexts when possible
>
> According to the EXT_color_buffer_half_float spec:
>
> "Dependencies on OES_texture_half_float
>
>     If OES_texture_half_float is not supported, then all references to
>     RGBA16F_EXT, RGB16F_EXT, RG16F_EXT, R16F_EXT, HALF_FLOAT_OES and
>     half should be ignored.
>
>     If OES_texture_half_float is supported, textures created with:
>
>         <internalformat> = RGBA
>         <format> = RGBA
>         <type> = HALF_FLOAT_OES
>
>     are renderable."
>
> This fixes 4 viz_unittests when running with SwANGLE:
>     All/GLI420ConverterPixelTest.ScaleAndConvert/0
>     All/GLI420ConverterPixelTest.ScaleAndConvert/1
>     GLScalerPixelTest.Example_ScaleAndExportForScreenVideoCapture
>     GLScalerPixelTest.ScalesWithColorManagement
>
> Bug: angleproject:5174
> Change-Id: If8623b1edbc8f0bac83513ea202ef49ad388101c
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2489726
> Commit-Queue: Alexis Hétu <sugoi@chromium.org>
> Reviewed-by: Geoff Lang <geofflang@chromium.org>

TBR=sugoi@chromium.org,geofflang@chromium.org,sugoi@google.com

Change-Id: Iab2df8ac563661fcf270425408b17e7bbe48a255
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:5174
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2490820Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>