powerpc: Drops STABS_DEBUG from linker scripts

No toolchain we support should be generating stabs debug information
anymore. Drop the sections entirely from our linker scripts.

We removed all the manual stabs annotations in commit
12318163 ("powerpc/32: Remove remaining .stabs annotations").

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220928130951.1732983-1-mpe@ellerman.id.au