worktree: accept -f as short for --force for removal

worktree: accept -f as short for --force for removal

Many commands support a "--force" option, frequently abbreviated as
"-f", however, "git worktree remove"'s hand-rolled OPT_BOOL forgets
to recognize the short form, despite git-worktree.txt documenting
"-f" as supported. Replace OPT_BOOL with OPT__FORCE, which provides
"-f" for free, and makes 'remove' consistent with 'add' option
parsing (which also specifies the PARSE_OPT_NOCOMPLETE flag).

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>