mbsync-idle: Avoid quotation marks on NOT DELETED.

imaplib2 automatically adds quotation marks around arguments that
contain spaces. This causes problems with some IMAP servers, such as
Google IMAP (GMail).

The symptoms are errors like:

    error: UID command error: BAD ['Error in IMAP command UID SEARCH: Unexpected string as search key: NOT DELETED']. Data: OMHI3 UID SEARCH "NOT DELETED"

By splitting 'NOT DELETED' into two arguments, the erroneous command

    A1 UID SEARCH "NOT DELETED"

becomes

    A1 UID SEARCH NOT DELETED

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>