Get rid of `CreateMutex` fallback entirely: Implement TryEnterCriticalSection for 9x/Me and NT<4

[seritools]

For 9x/ME:

Implement it similar to https://fanael.github.io/stockfish-on-windows-98.html#dynamic-dispatch. Another impl is in KernelEx

For NT before 4:

Reverse what NT4+ do. https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/pebteb/teb/index.htm shows that for NT3.1 CountOfOwnedCriticalSections didn't exist, or is potentially stored somewhere else. Figure out and implement the right fallback.

[seritools]

Can clean up the condvar impl here then, as well: https://github.com/rust9x/rust/blob/b16181952e83ed7b4089f26dc3843e3fd7385e5e/library/std/src/sys/sync/condvar/rust9x/legacy.rs

Actually, the SignalObjectAndWait branch is dead anyway, as any system supporting SignalObjectAndWait already uses MutexKind::CriticalSection or newer.