vconsole: Don't skip udev call for dummy device

Kernel 4.19 supports deferred console takeover [0], i.e., fbcon will
take over the console only when the first text is displayed on the
console. Before that event, only the dummy console is active. Our
currently udev rules call systemd-vconsole on every vtcon except for
dummy consoles. Thus the exception for dummy consoles prevents a call
to systemd-vconsole when no text is displayed on the console, and as a
consequence, the keymap will not be set in that case. This is wrong and
leads to issues when keyboard input is expected without text on the
console, e.g., when a graphical password prompt is used in the boot
process.

This reverts commit 6b169c13,
which introduced the exception for dummy devices to save unnecessary
udev calls.

Fixes #10826.

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=83d83bebf40132e2d55ec58af666713cc76f9764