phy: atheros: Make RGMII Tx delays actually configurable for AR8035

Delete the extraneous write to debug reg 5 that enables Tx delay

When the driver was originally introduced in commit "6027384a phylib:
Add Atheros AR8035 GETH PHY support", the Tx delay was being
unconditionally enabled.

Then during "2ec4d10b phy: atheros: add support for RGMII_ID, RGMII_TXID
and RGMII_RXID", the author did not notice that code for enabling Tx
delay code was already. Therefore, the if condition for Tx delay has
always been useless for this PHY since this commit introduced it.

Prior to this patch, every AR8035 PHY in U-boot had Tx delay enabled.
After this patch, only those who define the interface as RGMII_TXID or
RGMII_ID will. This is to be expected, but will nonetheless break the
setups of those who didn't know they rely on Tx delay implicitly.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>