oss: remove maui_boot.h from .gitignore and dontdiff

Commit d56b9b9c464a10ab1ee51a4c6190a2b57b8ef7a6 ("The scheduled removal
of some OSS drivers") removed all traces of maui_boot.h from the tree.
Remove its entries in dontdiff and oss's .gitignore file.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>