jtag/vdebug: remove BSD-2-Clause boilerplate

jtag/vdebug: remove BSD-2-Clause boilerplate

The full text of the license is already available in the file
	LICENSES/preferred/BSD-2-Clause
and there is no need to replicate it in the source code.

Remove the BSD-2-Clause boilerplate but, preserved the copyright
notice because it provides the info on the copyright holder.

Change-Id: I162aa4ad06b551f1a71a28d049cb797ee8ab5a01
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7146
Tested-by: jenkins
Reviewed-by: Jacek Wuwer <jacekmw8@gmail.com>