removal of bpf_tap() (not bpf_mtap)

[Masanobu SAITOH <msaitoh%execsw.org@localhost>]

 Hi.

 The following two changes removed bpf_tap() which uses linear data
instead of mbuf:

	http://mail-index.netbsd.org/source-changes/2018/06/22/msg096214.html
	http://mail-index.netbsd.org/source-changes/2018/06/22/msg096215.html

 Only above two drivers used bpf_tap(). There is no any driver
which use it now. Is it OK to remove from bpf.[ch]?

--
-----------------------------------------------
                SAITOH Masanobu (msaitoh%execsw.org@localhost
                                 msaitoh%netbsd.org@localhost)