mesa: Switch to the other glGetVertexAttribPointervARB implementation.

mesa: Switch to the other glGetVertexAttribPointervARB implementation.

Previously, Mesa used nvprogram.c's _mesa_GetVertexAttribPointervNV()
function to implement this GL call.  There was also a second
implementation in varray.c, _mesa_GetVertexAttribPointervARB(), which
was entirely unused.

The varray.c variant has an additional assertion and checks the index
against ctx->Const.VertexProgram.MaxAttribs rather than
MAX_VERTEX_GENERIC_ATTRIBS.  However, that variable is defined to the
same value, so it should be fine.

This will allow us to kill the duplicate function.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>