nb/intel/ironlake: Drop copy-pasted and dead code

nb/intel/ironlake: Drop copy-pasted and dead code

This function was copy-pasted, comments included, from Sandy Bridge.
However, it is only called with 0x0044 as the northbridge's PCI ID.
Therefore, `bridge_silicon_revision() & BASE_REV_MASK` will always
evaluate to 0x40, which never equals `BASE_REV_SNB`, that is, 0x00.
As the condition is always false, treat this code as dead and drop it.

Following a similar reasoning, all direct comparisons against SNB
steppings will always be true, because `bridge_silicon_revision()`
returns at least 0x40 which is always larger than either `SNB_STEP_D0`
or `SNB_STEP_D1`. So, drop all but the code path that is actually used.

Change-Id: I5219a6af3df98ed77c9c4abfb9a63c2ebf8171bb
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42697
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>