MAINTAINERS: Remove Linux / PowerPC maintainer

See: [FFmpeg-devel] PPC64: PowerPC Maintainer information is incorrect
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

MAINTAINERS

@@ -552,7 +552,6 @@ AVR32                                   Mans Rullgard
 MIPS                                    Mans Rullgard, Nedeljko Babic
 Mac OS X / PowerPC                      Romain Dolbeau, Guillaume Poirier
 Amiga / PowerPC                         Colin Ward
-Linux / PowerPC                         Luca Barbato
 Windows MinGW                           Alex Beregszaszi, Ramiro Polla
 Windows Cygwin                          Victor Paesa
 Windows MSVC                            Matthew Oliver, Hendrik Leppkes