scripts: remove gdb from Python requirements file

This package is no longer available in PyPI.

Signed-off-by: Karol Latecki <karol.latecki@intel.com>
Change-Id: I3e68b03eabeb4aff14453c90846fd03452c93ae2
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/8956


Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Community-CI: Mellanox Build Bot
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>