Simplify build_sparkle_framework.py

Add GN target for tarring our Sparkle binaries

Add GN target for tarring our Sparkle binaries

The produced .tar.gz then gets included in Brave, which is particularly
useful for cross-compiling from Linux to macOS.

Add file forgotten in previous commit

Remove obsolete build files

We previously included Sparkle as a DEP. Now, we depend on pre-built
binaries. For that reason, the files that were necessary for inclusion
as a DEP are no longer needed.