sys/syz-extract: don't redefine __asm__ in ELF mode
sys/syz-extract: don't redefine __asm__ in ELF mode

This is not necessary since we build legit object file
for the target binary now. But this breaks mips with:

/linux/arch/mips/include/asm/thread_info.h:53:30: error: register name not specified for ‘__current_thread_info’
 register struct thread_info *__current_thread_info __asm__("$28");

So just remove the old hack.

Follow up to #1536

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