Amend python pkgs for debian-based distros

Drop python2 packages that are no longer needed. Replace other py2 pkgs
with their py3 variant.

Change-Id: Id5fc11d1ae0a7daf439c7d72f831f298f5d0ce31
diff --git a/files/debs/neutron-common b/files/debs/neutron-common
index b269f63..e548396 100644
--- a/files/debs/neutron-common
+++ b/files/debs/neutron-common
@@ -9,7 +9,7 @@
 libmysqlclient-dev
 mysql-server #NOPRIME
 postgresql-server-dev-all
-python-mysqldb
+python3-mysqldb
 rabbitmq-server # NOPRIME
 radvd # NOPRIME
 sqlite3