mmc: sdhci: Drop redundant code for SDIO IRQs

Nowadays sdhci prevents runtime suspend when SDIO IRQs are enabled.

However, some variants such as sdhci-esdhc-imx's, tries to allow runtime
suspend while having the SDIO IRQs enabled, but without supporting remote
wakeups. This support is a bit questionable, especially if the host device
have a PM domain attached that can be power gated, but more importantly,
the code have also become redundant (which was not the case when it was
introduced).

Rather than keeping the redundant code around, let's drop it and leave this
to be revisited later on.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>