fix: follow autoconf conventions for --enable/--disable help output

[kurok]

Summary

• Change --enable-liblsof to --disable-liblsof in help output (feature is enabled by default)
• Remove redundant [default=no] from --enable-security and --enable-no-sock-security

Motivation

Per GNU autoconf conventions, ./configure --help should show:

• --disable-X for features that are enabled by default (user needs to know how to turn it off)
• --enable-X for features that are disabled by default (user needs to know how to turn it on)

No [default=...] annotation is needed — the option direction already communicates the default.

Before:

  --enable-liblsof        build and install liblsof [default=yes]
  --enable-security       allow only the root user to list all open files [default=no]
  --enable-no-sock-security
                          combined with --enable-security, allow anyone to
                          list anyone else's socket files [default=no]

After:

  --disable-liblsof       do not build and install liblsof
  --enable-security       allow only the root user to list all open files
  --enable-no-sock-security
                          combined with --enable-security, allow anyone to
                          list anyone else's socket files

Only configure.ac is changed (4 lines). No build logic is affected — only the help text.

Closes #325