[CodeGen] [WinException] Remove a redundant explicit section switch for aarch64

The following EmitWinEHHandlerData() implicitly switches to .xdata, just
like on x86_64.

This became orphaned from the original code requiring it in
0b61d220 / https://reviews.llvm.org/D61095.

Differential Revision: https://reviews.llvm.org/D87447