pkg/csource: don't test auto-generated files
pkg/csource: don't test auto-generated files

syz_mount_image tests are very large and TestSysTests takes too long.
syz-imagegen that generates them does some of this testing
(Deserialize/SerializeForExec).

xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller