[InstrProfiling] Delete linkage/visibility toggling for Windows

The linkage/visibility of `__profn_*` variables are derived
from the profiled functions.

    extern_weak => linkonce
    available_externally => linkonce_odr
    internal => private
    extern => private
    _ => unchanged

The linkage/visibility of `__profc_*`/`__profd_*` variables are derived from
`__profn_*` with linkage/visibility wrestling for Windows.

The changes can be folded to the following without changing semantics.

```
if (TT.isOSBinFormatCOFF() && !NeedComdat) {
  Linkage = GlobalValue::InternalLinkage;
  Visibility = GlobalValue::DefaultVisibility;
}
```

That said, I think we can just delete the code block.

An extern/internal function will now use private `__profc_*`/`__profd_*`
variables, instead of internal ones. This saves some symbol table entries.

A non-comdat {linkonce,weak}_odr function will now use hidden external
`__profc_*`/`__profd_*` variables instead of internal ones.  There is potential
object file size increase because such symbols need `/INCLUDE:` directives.
However such non-comdat functions are rare (note that non-comdat weak
definitions don't prevent duplicate definition error).

The behavior changes match ELF.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D103355