Remove Q_PACKED from structs that don't need to be packed

Remove Q_PACKED from structs that don't need to be packed

Those classes don't contain padding, they don't need to be packed. The
only reason to be packed was to deal with bad alignment of the WAV
file.

Since Q_PACKED wasn't present in all compilers, this might have been a
latent bug. If that was the case, then force it to happen with more
compilers.

Change-Id: I8449b6bab5d62c1b7e08b9bc205b4b149ed55e28
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>