Remove unused-variable in velox/experimental/wave/exec/ToWave.cpp +3 (f…

…acebookincubator#11504)

Summary:
Pull Request resolved: facebookincubator#11504

LLVM-15 has a warning `-Wunused-variable` which we treat as an error because it's so often diagnostic of a code issue. Unused variables can compromise readability or, worse, performance.

This diff either (a) removes an unused variable and, possibly, it's associated code or (b) qualifies the variable with `[[maybe_unused]]`.

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Differential Revision: D65755246

fbshipit-source-id: 8dfce093a9c638f0630fe7460a029f266083c834

velox/experimental/wave/exec/ToWave.cpp

@@ -625,7 +625,6 @@ bool isProjectedThrough(
 
 bool CompileState::compile() {
   auto operators = driver_.operators();
-  auto& nodes = driverFactory_.planNodes;
 
   int32_t first = 0;
   int32_t operatorIndex = 0;