wlanap.cgi: Access db.txt in place of using regdbdump on regulatory.bin

wlanap.cgi: Access db.txt in place of using regdbdump on regulatory.bin

- wlanap.cgi was using regdbdump from crda to create a text based list of the
   wireless settings by country database.
- With the removal of crda as part of the removal of python2 this option could not be
   used.
- wireless-regdb also has a text based database list in the source tarball and this
   patch makes wlanap.cgi read this list into the @countrylist_cmd variable
- This needs to be tested by someone that has an IPFire system with wifi that can access
   and evaluate wlanap.cgi to confirm that this change functions as expected.
- This version changes the name of the stored text file from db.txt to regulatorydb.txt
- The command to read the data from regulatorydb.txt into @countrylist_cmd has been
   corrected

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Bernhard Bitsch <bbitsch@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>