library.pl: Remove invalid archs for buster

As reported in https://github.com/docker-library/official-images/actions/runs/3972788175/jobs/6810987892

Author: zakame

library.pl

@@ -9,7 +9,7 @@
 
   # https://github.com/docker-library/official-images/blob/master/library/debian
   bullseye => 'amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, s390x',
-  buster => 'amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, s390x',
+  buster => 'amd64, arm32v7, arm64v8, i386',
 );
 
 print <<"END_HEADER";