Remove residual blank line at start of Makefile

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

if_tuntap: remove if_{tun,tap}.ko -> if_tuntap.ko links

These drivers have been merged into a single if_tuntap in 13.0. The
compatibility links existed only for the interim and will be MFC'd along
w

if_tuntap: remove if_{tun,tap}.ko -> if_tuntap.ko links

These drivers have been merged into a single if_tuntap in 13.0. The
compatibility links existed only for the interim and will be MFC'd along
with the if_tuntap merge shortly.

MFC after: never

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MFHead @347527

Sponsored by: The FreeBSD Foundation

tun/tap: merge and rename to `tuntap`

tun(4) and tap(4) share the same general management interface and have a lot
in common. Bugs exist in tap(4) that have been fixed in tun(4), and
vice-versa. Let

tun/tap: merge and rename to `tuntap`

tun(4) and tap(4) share the same general management interface and have a lot
in common. Bugs exist in tap(4) that have been fixed in tun(4), and
vice-versa. Let's reduce the maintenance requirements by merging them
together and using flags to differentiate between the three interface types
(tun, tap, vmnet).

This fixes a couple of tap(4)/vmnet(4) issues right out of the gate:
- tap devices may no longer be destroyed while they're open [0]
- VIMAGE issues already addressed in tun by kp

[0] emaste had removed an easy-panic-button in r240938 due to devdrn
blocking. A naive glance over this leads me to believe that this isn't quite
complete -- destroy_devl will only block while executing d_* functions, but
doesn't block the device from being destroyed while a process has it open.
The latter is the intent of the condvar in tun, so this is "fixed" (for
certain definitions of the word -- it wasn't really broken in tap, it just
wasn't quite ideal).

ifconfig(8) also grew the ability to map an interface name to a kld, so
that `ifconfig {tun,tap}0` can continue to autoload the correct module, and
`ifconfig vmnet0 create` will now autoload the correct module. This is a
low overhead addition.

(MFC commentary)

This may get MFC'd if many bugs in tun(4)/tap(4) are discovered after this,
and how critical they are. Changes after this are likely easily MFC'd
without taking this merge, but the merge will be easier.

I have no plans to do this MFC as of now.

Reviewed by: bcr (manpages), tuexen (testing, syzkaller/packetdrill)
Input also from: melifaro
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D20044

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