[libunwind] Remove needless `sys/uio.h` (#97495)

No reference to `readv` or `writev`. This makes `libcxx` happy when
compiling against clang's `libc` as part of
https://github.com/llvm/llvm-project/issues/97191.

NOKEYCHECK=True
GitOrigin-RevId: 495452e7da8fad7bd311fd041530d72c101da643
1 file changed
tree: b0cebd1bf133c280b524c4f7e4afd27492956aed
  1. cmake/
  2. docs/
  3. include/
  4. src/
  5. test/
  6. .clang-format
  7. CMakeLists.txt
  8. LICENSE.TXT