package/gdb: drop support for version 8.3.x

Now that gdb 11.x has been added, that 10.x is the default, we can
drop version 8.3.x.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>