[ProfileData] Remove swapToHostOrder (#94665)

This patch removes swapToHostOrder in favor of
llvm::support::endian::readNext as swapToHostOrder is too thin a
wrapper around readNext.

Note that there are two variants of readNext:

- readNext<type, endian, align>(ptr)
- readNext<type, align>(ptr, endian)

swapToHostOrder uses the former, but this patch switches to the latter.

While we are at it, this patch teaches readNext to default to
unaligned just as I did in:

  commit 568368a4
  Author: Kazu Hirata <kazu@google.com>
  Date:   Mon Apr 15 19:05:30 2024 -0700