[FIX] l10n_lu: taxes (amont/aval)

The accounts "TVA en amont" were not used by the l10n_lu chart of accounts.

Instead the accounts "TVA en aval" were used for all taxes both sale and purchase taxes.

(Manual rebase of PR #735)
[FIX] l10n_lu: wrong mapping of accounts to P&L financial report

Account 655 and its child 6554 were both mapped.
Fixed by unmapping 655 and mapping all its direct children.

(Manual rebase of PR #733)