delete observe from the repo

pkg/observe/PATENTS

-Additional IP Rights Grant (Patents)
-
-"This implementation" means the copyrightable works distributed by
-Google as part of the Dart Project.
-
-Google hereby grants to you a perpetual, worldwide, non-exclusive,
-no-charge, royalty-free, irrevocable (except as stated in this
-section) patent license to make, have made, use, offer to sell, sell,
-import, transfer, and otherwise run, modify and propagate the contents
-of this implementation of Dart, where such license applies only to
-those patent claims, both currently owned by Google and acquired in
-the future, licensable by Google that are necessarily infringed by
-this implementation of Dart. This grant does not include claims that
-would be infringed only as a consequence of further modification of
-this implementation. If you or your agent or exclusive licensee
-institute or order or agree to the institution of patent litigation
-against any entity (including a cross-claim or counterclaim in a
-lawsuit) alleging that this implementation of Dart or any code
-incorporated within this implementation of Dart constitutes direct or
-contributory patent infringement, or inducement of patent
-infringement, then any patent rights granted to you under this License
-for this implementation of Dart shall terminate as of the date such
-litigation is filed.