[InstCombine] Remove SPF guard for trunc transforms (#117535)

This shouldn't be necessary anymore now that SPF patterns are
canonicalized to intrinsics.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -786,15 +786,6 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
     }
   }
 
-  // Test if the trunc is the user of a select which is part of a
-  // minimum or maximum operation. If so, don't do any more simplification.
-  // Even simplifying demanded bits can break the canonical form of a
-  // min/max.
-  Value *LHS, *RHS;
-  if (SelectInst *Sel = dyn_cast<SelectInst>(Src))
-    if (matchSelectPattern(Sel, LHS, RHS).Flavor != SPF_UNKNOWN)
-      return nullptr;
-
   // See if we can simplify any instructions used by the input whose sole
   // purpose is to compute bits we don't care about.
   if (SimplifyDemandedInstructionBits(Trunc))