[llvm] [AMDGPU] Remove duplicated/confusing helpers. NFCI (PR #142598)

[Matt Arsenault via llvm-commits]

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@@ -1145,7 +1129,8 @@ bool AMDGPUCallLowering::isEligibleForTailCallOptimization(
 
   // If we have -tailcallopt, then we're done.
   if (MF.getTarget().Options.GuaranteedTailCallOpt)
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arsenm wrote:

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https://github.com/llvm/llvm-project/pull/142598