i386: Remove CET support

i386: Remove CET support

CET is only support for x86_64, this patch reverts:

  - faaee1f07ed x86: Support shadow stack pointer in setjmp/longjmp.
  - be9ccd27c09 i386: Add _CET_ENDBR to indirect jump targets in
    add_n.S/sub_n.S
  - c02695d7764 x86/CET: Update vfork to prevent child return
  - 5d844e1b725 i386: Enable CET support in ucontext functions
  - 124bcde683 x86: Add _CET_ENDBR to functions in crti.S
  - 562837c002 x86: Add _CET_ENDBR to functions in dl-tlsdesc.S
  - f753fa7dea x86: Support IBT and SHSTK in Intel CET [BZ #21598]
  - 825b58f3fb i386-mcount.S: Add _CET_ENDBR to _mcount and __fentry__
  - 7e119cd582 i386: Use _CET_NOTRACK in i686/memcmp.S
  - 177824e232 i386: Use _CET_NOTRACK in memcmp-sse4.S
  - 0a899af097 i386: Use _CET_NOTRACK in memcpy-ssse3-rep.S
  - 7fb613361c i386: Use _CET_NOTRACK in memcpy-ssse3.S
  - 77a8ae0948 i386: Use _CET_NOTRACK in memset-sse2-rep.S
  - 00e7b76a8f i386: Use _CET_NOTRACK in memset-sse2.S
  - 90d15dc577 i386: Use _CET_NOTRACK in strcat-sse2.S
  - f1574581c7 i386: Use _CET_NOTRACK in strcpy-sse2.S
  - 4031d7484a i386/sub_n.S: Add a missing _CET_ENDBR to indirect jump
  - target
  -
Checked on i686-linux-gnu.