Remove enable_swiftshader=false from GN flags
Remove enable_swiftshader=false from GN flags

This addresses
https://github.com/ungoogled-software/ungoogled-chromium-macos/issues/24,
which requires enable_swiftshader=true. There is no strong reason in terms
of the project's objectives to disable SwiftShader, so it will be moved
to the platform-specific flags.

Eloston/ungoogled-chromium,Eloston/ungoogled-chromium