[polly] Remove unused variable in ScopBuilder.cpp (NFC)

/llvm-project/polly/lib/Analysis/ScopBuilder.cpp:2725:18:
error: unused variable 'DT' [-Werror,-Wunused-variable]
  DominatorTree *DT = Stmt.getParent()->getDT();
                 ^
1 error generated.
GitOrigin-RevId: 3ab0e958cc9338a8435ae29f9d381395aaba03c6
1 file changed