Remove -fsjlj-exceptions from win32-config

This seems to be missing using i686-w64-mingw32/10-posix after updating release images to Debian 11.

It is not clear why this flag was added in the first place for win32 but not win64.

Context: https://stackoverflow.com/questions/61206449/how-to-compile-with-clang-and-mingw-w64
PiperOrigin-RevId: 651545252

toolchain/BUILD.bazel

@@ -133,7 +133,6 @@ cc_toolchain_config(
     extra_compiler_flags = [
         "-isystem/usr/lib/gcc/i686-w64-mingw32/10-posix/include/c++",
         "-isystem/usr/lib/gcc/i686-w64-mingw32/10-posix/include/c++/i686-w64-mingw32",
-        "-fsjlj-exceptions",
     ],
     extra_include = "/usr/lib/gcc/i686-w64-mingw32",
     extra_linker_flags = [