security/stoken: unbreak build with LLVM >= 17 (+)

FreeBSD already have strcasestr() and mkstemps() functions and compat stubs
are always skipped so declare local functions in map file is false positive.

LLVM >= 17 is more restrictive with declared but missed functions which lead to linker error.

Drop local stubs stokenstrcasestr() and stokenmkstemps() from library map file to unbreak.

Reported by: poudriere failure
Approved by: portmgr blanket (trivial build fix)