edk2: Move TianoCore Contribution Agreement to root

https://bugzilla.tianocore.org/show_bug.cgi?id=629



Move Contributions.txt that contains the TianoCore
Contribution Agreement 1.0 to the root of the edk2
repository and remove the duplicate Contributions.txt
files from all packages.

Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Andrew Fish <afish@apple.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>