refs: #12219

Remove the feature-12373-honor-debug-kernel-cmdline APT overlay: superseded by new package in the feature-stretch suite.

Fix-committed: #12373

Closes: #12260, #12369

KeePassX wrapper: document the (shared) purpose of two somewhat obscure lines of code (refs: #12369).

Without this change, after importing one's v1 DB, one would be prompted to
re-import it every time they start KeePassX again if they saved their new DB
under a name that's neither "New database.kdbx" nor "keepassx.kdbx".

Let's not even go through the migration code if there's already a new-style DB.

The .desktop file has "Exec=keepassx %f".