Do not set mediump precision on vertex shaders

[greggman]

vertex shaders in webgl default to highp

#8627

[kripken]

cc @kenrussell @kainino0x @juj

[kainino0x]

This looks correct to me, but I also don't know why this code was written in the first place.

Can you remove ensurePrecision as well? It seems unused.

[greggman]

ensurePrecision was used for both vertex and fragment shaders. This PR removes its usage for vertex shaders where it's not needed.

[kainino0x]

Ah, sorry, I tried to search for other usages and I failed. LGTM

[juj]

This looks correct to me, but I also don't know why this code was written in the first place.

This change relates to legacy GL emulation, where source fragment shaders may come in without a precision qualifier, but in WebGL fragment shaders, precision qualifiers are mandatory. So to emulate, one is added automatically.

LGTM to remove the precision qualifier from WebGL vertex shaders, that is not required (unlike WebGL fragment shaders do)