kernel: Remove CONFIG_BLK_DEV_RAM=y (remove /dev/ram* devices)
kernel: Remove CONFIG_BLK_DEV_RAM=y (remove /dev/ram* devices)

This option allows to use portions of the system RAM as block devices.
It was configured to 'y' (built-in, therefore not unloadable or
reconfigurable) and configured 16 4MB RAM disks which, to my knowledge,
currently have no purpose in NixOS.

Removing the option restores it to it's default value of 'm', which
enables it to be loaded at runtime (which is also required to be able to
change it's configuration without rebuilding the kernel).

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