[BACKEND] Disable BreakPhiStruct pass (#2458)

This is causing functional failures in pytorch workload. Disabling it
until I figure out the problem.

lib/Target/LLVMIR/LLVMIRTranslation.cpp

@@ -122,14 +122,6 @@ makeOptimizingPipeline(unsigned optLevel, unsigned sizeLevel,
     pb.crossRegisterProxies(lam, fam, cgam, mam);
 
     ModulePassManager mpm;
-    pb.registerVectorizerStartEPCallback(
-        [&](llvm::FunctionPassManager &fpm, llvm::OptimizationLevel level) {
-          // Triton generates large structure of scalars which may pessimise
-          // optimizations, we run a pass to break up phi of struct to make sure
-          // all the struct are removed for the following passes.
-          fpm.addPass(BreakStructPhiNodesPass());
-          fpm.addPass(InstCombinePass());
-        });
     mpm.addPass(pb.buildPerModuleDefaultPipeline(*ol));
     mpm.run(*m, mam);
     return Error::success();