ravb: Remove checks for unsupported internal delay modes

The EtherAVB instances on the R-Car E3/D3 and RZ/G2E SoCs do not support
TX clock internal delay modes, and the EtherAVB driver prints a warning
if an unsupported "rgmii-*id" PHY mode is specified, to catch buggy
DTBs.

Commit a6f51f2e ("ravb: Add support for explicit internal
clock delay configuration") deprecated deriving the internal delay mode
from the PHY mode, in favor of explicit configuration using the now
mandatory "rx-internal-delay-ps" and "tx-internal-delay-ps" properties,
thus delegating the warning to the legacy fallback code.

Since explicit configuration of a (valid) internal clock delay
configuration is enforced by validating device tree source files against
DT binding files, and all upstream DTS files have been converted as of
commit a5200e63

 ("arm64: dts: renesas: rzg2: Convert EtherAVB to
explicit delay handling"), the checks in the legacy fallback code can be
removed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/2037542ac56e99413b9807e24049711553cc88a9.1628696778.git.geert+renesas@glider.be
Signed-off-by: Jakub Kicinski <kuba@kernel.org>