metadata: minor variable cleanup

Keep variables locals if we can, and give them specific names to make
the code easier to read.

Fix a small typo in kdbus.txt while at it.

Signed-off-by: Daniel Mack <daniel@zonque.org>
queue: drop unused function parameter

kdbus_queue_entry_move() doesn't use its first parameter 'conn_src'
for anything, so drop it.

Signed-off-by: Daniel Mack <daniel@zonque.org>