Don’t distinguish between BSD and non-BSD manuals.

There's not really a need to distinguish these in the doctools package.

- rename *.[17]b to *.[17]
- install manpages to man[17] instead of man[17b]
- remove “(BSD)” and “/usr/ucb” from NAME and SYNOPSIS sections
- replace references to foo(1B) and foo(7B) with foo(1) and foo(7)