devel/bitkeeper: Symlink to bin/bk does not work

The bitkeeper binary, bk, checks whether the path from which it was
executed is a symbolic link and if it is, it terminates with an error.
Remove the symlink and add a pkg-message telling the user to add
${LOCALBASE}/bitkeeper/bin to their path.

PR: 247160
Reported by: Gian-Simon Purkert <gspurki@gmail.com>