net: ipa: remove unneeded FILT_ROUT_HASH_EN definitions

The FILT_ROUT_HASH_EN register is only used for IPA v4.2.  There,
routing and filter table hashing are not supported, and so the
register must be written to disable the feature.  No other version
uses this register, so its definition can be removed.  If we need to
use these some day (for example, explicitly enable the feature) this
commit can be reverted.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>