Remove $FreeBSD$: one-line sh pattern

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

ddb: use 'textdump dump' instead of 'call doadump'

The change is for the example in textdump.4 and the default ddb.conf.

First of all, doadump now requires an argument and it won't do a
textdump if the argument is not 'true'.
And 'textdump dump' is more idiomatic anyway.

For what it's worth, ddb 'dump' command seems to always request a vmcore
dump even if a textdump was requested earlier, e.g., by 'textdump set'.
Finally, ddb 'call' command is not documented.

MFC after: 2 weeks

Move ddb.conf to sbin/ddb/ and switch to CONFS.

This helps pkgbase as this config file will now be tagged as a config file.

Approved by: allanjude (mentor)
Differential Revision: https://reviews.freebsd.org/D16675