Revert "scripts: mandate that new files have SPDX-License-Identifier"

Revert "scripts: mandate that new files have SPDX-License-Identifier"

This reverts commit fa4d79c64dae03ffa269e42e21822453856618b7.

The logic in this commit was flawed in two critical ways

 * It always failed to report SPDX validation on the last newly
   added file. IOW, it only worked if at least 2 new files were
   added in a commit

 * If an existing file change, followed a new file change, in
   the commit and the existing file context/changed lines
   included SPDX-License-Identifier, it would incorrectly
   associate this with the previous newly added file.

Simply reverting this commit will make it significantly easier to
understand the improved logic in the following commit.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>