[PlaceSafepoints] Entry safepoint location doesn't need to be a terminator
[PlaceSafepoints] Entry safepoint location doesn't need to be a terminator

Long ago, the poll insertion code assumed that the insertion site was a terminator.  As a result, the entry selection code would split a basic block to ensure it could pass a terminator.  The insertion code was updated quite a while ago - possibly before it ever landed upstream - but the now redundant work was never removed.  

While I'm at it, remove a comment which doesn't apply to the upstreamed code.  

NFC intended.



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@238254 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,dslab-epfl/asap,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap