parser_bison: Fix for deprecated statements

parser_bison: Fix for deprecated statements

Bison-3.3 started to warn about:

/home/n0-1/git/nftables/src/parser_bison.y:117.1-19: warning: deprecated directive, use ‘%define api.prefix {nft_}’ [-Wdeprecated]
    117 | %name-prefix "nft_"
        | ^~~~~~~~~~~~~~~~~~~
/home/n0-1/git/nftables/src/parser_bison.y:119.1-12: warning: deprecated directive, use ‘%define api.pure’ [-Wdeprecated]
  119 | %pure-parser
      | ^~~~~~~~~~~~
/home/n0-1/git/nftables/src/parser_bison.y:124.1-14: warning: deprecated directive, use ‘%define parse.error verbose’ [-Wdeprecated]
  124 | %error-verbose
      | ^~~~~~~~~~~~~~

Replace the last two as suggested but leave the first one in place as
that causes compilation errors in scanner.l - flex seems not to pick up
the changed internal symbol names.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>