[llvm] [ConstantFPRange] Remove `ConstantFPRange::toKnownFPClass` (PR #109960)

[Matt Arsenault via llvm-commits]

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@@ -196,13 +196,6 @@ FPClassTest ConstantFPRange::classify() const {
   return static_cast<FPClassTest>(Mask);
 }
 
-KnownFPClass ConstantFPRange::toKnownFPClass() const {
-  KnownFPClass Result;
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arsenm wrote:

Which reminds me, we for some reason have llvm/ADT/FloatingPointMode.h, and llvm/IR/FPEnv.h. I can't tell if there's some intentional split here 

https://github.com/llvm/llvm-project/pull/109960