In parsec v2, merge_local_folder_manifest accept local manifest with arbitrary prevent sync pattern.

The idea was it was a very unlikely event (a new prevent sync pattern have been set and is not fully applied), and in this case a flag could be passed to tell merge_local_folder_manifest to manually apply the new prevent sync pattern to local

In practice however this was not needed since the prevent sync pattern is only set when starting the WorskpaceFS, which in turn ensure the prevent sync pattern is fully applied as part of it initialization routine

On top of that, having merge_local_folder_manifest accepting outdated local makes the function significantly harder to test (see https://github.com/Scille/parsec-cloud/pull/7756/files#diff-4e496067608e0a1d8d2067e4121b7465f612c1007dc9f35128cf0054ab3adc99R605-R625)

So we could simplify this by just considering merge_local_folder_manifest only accept local manifest in sync with prevent_sync_pattern (and adding a docstring to this fonction to document this !)