Make kasp2policy.py PyLint-clean

PyLint 2.9.5 reported the following errors:

contrib/kasp/kasp2policy.py:25:0: R0402: Use 'from ply import yacc' instead (consider-using-from-import)
contrib/kasp/kasp2policy.py:26:0: R0402: Use 'from ply import lex' instead (consider-using-from-import)

• ~"v9.17" - https://gitlab.isc.org/isc-projects/bind9/-/jobs/1893293 (no change needed)
• v9.16 - https://gitlab.isc.org/isc-projects/bind9/-/jobs/1893582
• v9.16-S - https://gitlab.isc.org/isc-private/bind9/-/jobs/1893773
• ~"v9.11" - https://gitlab.isc.org/isc-projects/bind9/-/jobs/1893584
• ~"v9.11-S" - https://gitlab.isc.org/isc-private/bind9/-/jobs/1893774

The PyLint change should be actually made in the images repo: https://gitlab.isc.org/isc-projects/images/-/merge_requests/128.