Fix warning by removing unused variable (#81604)

Apparently, some compilers [correctly] warn that the variable that was
created prior to this change is unused.

This reemoves the variable.

Author: Leporacanthicus

flang/lib/Semantics/canonicalize-omp.cpp

@@ -92,7 +92,7 @@ class CanonicalizationOfOmp {
     nextIt = it;
     while (++nextIt != block.end()) {
       // Ignore compiler directives.
-      if (auto *directive{GetConstructIf<parser::CompilerDirective>(*nextIt)})
+      if (GetConstructIf<parser::CompilerDirective>(*nextIt))
         continue;
 
       if (auto *doCons{GetConstructIf<parser::DoConstruct>(*nextIt)}) {