[MachineOutliner][NFC] Remove buildCandidateList and replace with findCandidates
[MachineOutliner][NFC] Remove buildCandidateList and replace with findCandidates

More refactoring.

Since the pruning logic has changed, and the candidate list is gone,
everything can be sunk into findCandidates.

We no longer need to keep track of the length of the longest substring, so we
can drop all of that logic as well.

After this, we just find all of the candidates and move to outlining.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@348428 91177308-0d34-0410-b5e6-96231b3b80d8

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