[SimplifyLibCalls] Removed some TODOs which are already implemented. NFC.
[SimplifyLibCalls] Removed some TODOs which are already implemented. NFC.

Summary:
D14302 implements tan(atan(x)) -> x
D14045 implements pow(exp(x), y) -> exp(x*y)

Patch by Mandeep Singh Grang <mgrang@codeaurora.org>

Reviewers: majnemer, davide

Differential Revision: http://reviews.llvm.org/D14882

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@253768 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm