Remove old GetTickCount() code path for Windows

Windows XP support was dropped since GHC 8.0 as per https://ghc.haskell.org/trac/ghc/wiki/WindowsGhc

In HsWord64 getMonotonicNSec() on Windows we still fall back to the 32-bit GetTickCount() if QueryPerformanceFrequency() is not supported: Code

But Microsoft's documentation says that QueryPerformanceFrequency() is guaranteed to be supported on Windows >= XP:

On systems that run Windows XP or later, the function will always succeed and will thus never return zero.

Thus we can remove the if (!qpc_supported) check and all if (!qpc_frequency.QuadPart) code paths, and replace it with an assertion or a ./configure check.

We can also add a comment that getMonotonicNSec() will indeed always make use of the whole 64-bit domain.

Trac metadata

Trac field	Value
Version	8.3
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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CC	bgamari, nh2
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