perf/marvell_cn10k: Remove useless license text when SPDX-License-Identifier is already used

An SPDX-License-Identifier is already in place. There is no need to
duplicate part of the corresponding license.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/4a8016a6da9cc6815cfa0f97ae8d3dd862797bda.1654936653.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Will Deacon <will@kernel.org>