i965: Drop index buffer re-alignment code.

i965: Drop index buffer re-alignment code.

This shouldn't ever happen - GL requires it to be aligned:

   "Clients must align data elements consistent with the requirements
    of the client platform, with an additional base-level requirement
    that an offset within a buffer to a datum comprising N basic
    machine units be a multiple of N."

Mesa should reject unaligned index buffers for us - we shouldn't have
to handle them in the driver.

Note that Gallium already makes this assumption.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>