This reverts commit 58f96be2c4.
This caused material files to increase in size significantly. It turns
out that glslang has to generate a copy for each parameter that is
passed to a function as a non-const parameter.
This revert will break IMG devices again, but that should be the case
only on debug builds. Release builds lose the const qualifier by
virtue of going through spirv. We'll try to address this some other
way later.
cd7973bdcf