sstate: Remove master manifest usage

sstate: Remove master manifest usage

This was added to allow detection of duplicate files being installed by sstate.
There is a much simpler way, just check if the file already exists. This
effectively uses the kernel VFS as the cache which is much more efficient.

This resolves a significant performance bottleneck (lock contention on a
single file) when running builds that are just being generated from sstate
cache files.

(From OE-Core rev: 603daf343ad3f18c8adb799e3625ae2a18d94f56)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>