[NFC] Deduplicate comment in PromoteMemoryToRegister.cpp

This has been duplicated since before
2372a19, but that commit has it
appearing twice in the space of 10 lines of the same function body. It
could also be hoisted up to the point just after where the last
special-case is considered, but I want to keep the intent of the
original authors.

Committed as obvious without a review.

Author: slinder1

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

@@ -595,11 +595,6 @@ void PromoteMem2Reg::run() {
     // Keep the reverse mapping of the 'Allocas' array for the rename pass.
     AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
 
-    // At this point, we're committed to promoting the alloca using IDF's, and
-    // the standard SSA construction algorithm.  Determine which blocks need PHI
-    // nodes and see if we can optimize out some work by avoiding insertion of
-    // dead phi nodes.
-
     // Unique the set of defining blocks for efficient lookup.
     SmallPtrSet<BasicBlock *, 32> DefBlocks(Info.DefiningBlocks.begin(),
                                             Info.DefiningBlocks.end());