The purpose of this function is to return the most fundamental path
without leaving a filesystem.  Steam uses this so that it can use inode
searches, without this functionality some installations/validations will
fail if the Steam Library is not on the same drive as Steam
itself (symlink'd to another location).

This reverts commit 443ef6e7.
The tests fail on all versions of Windows.

Based on patch by Huw Davies.

It's unnecessary since the vertex shader is going to change and
shader_glsl_select() flags all the constants used by the shader anyway.