imx-base.inc: Drop redundant i.MX 91 override

IMX_SOC_REV defaults to A0, so no need to override it.

Signed-off-by: Tom Hochstein <tom.hochstein@nxp.com>

conf/machine/include/imx-base.inc

@@ -184,7 +184,6 @@ IMX_SOC_REV:mx8dx-generic-bsp  ??= "C0"
 IMX_SOC_REV:mx8ulp-generic-bsp ??= \
     "${@bb.utils.contains('MACHINE_FEATURES', 'soc-reva0', 'A0', \
                                                            'A2', d)}"
-IMX_SOC_REV:mx91-generic-bsp   ??= "A0"
 IMX_SOC_REV:mx93-generic-bsp   ??= "A1"
 
 IMX_SOC_REV_LOWER   = "${@d.getVar('IMX_SOC_REV').lower()}"