[Support] [Windows] Stop redefining _WIN32_IE (#102307)
This was added in 181fd8cd89ff97fe654fabbb2032e0ad6607b4d0, where the
shlobj.h header was taken into use. The shlobj.h header does have some
APIs conditionally visible based on the _WIN32_IE define, but none of
the calls added in that commit seem to need any specific version.
fd6cb64c4891301648e5ab814afdafa118977c3d and
6b129bd464831194da957b3462d7ddd27a0b2a08 further bumped the version it
is set to, while the latter also added a FIXME to check whether it still
is needed.
It doesn't seem to be needed currently; the code currently builds fine
without this define, both with mingw-w64 and MSVC.
Additionally, to show that the value of _WIN32_IE doesn't seem to be
relevant to our builds these days - if the current define is changed to
hardcode _WIN32_IE to an ancient value like 0x0400, our code still
builds fine, both with mingw-w64 and MSVC. Therefore, overriding this
define no longer seem to be relevant.
