[llvm] [VPlan] Remove CanonicalIV when dissolving loop regions (NFC). (PR #142372)

[David Sherwood via llvm-commits]

david-arm wrote:

Looks like there are build failures:

```
C:\ws\src\llvm\lib\Transforms\Vectorize\VPlan.cpp(889): error C3861: 'Builder': identifier not found
C:\ws\src\llvm\lib\Transforms\Vectorize\VPlan.cpp(892): error C3536: 'ScalarR': cannot be used before it is initialized
C:\ws\src\llvm\lib\Transforms\Vectorize\VPlan.cpp(892): error C2664: 'void llvm::VPValue::replaceAllUsesWith(llvm::VPValue *)': cannot convert argument 1 from 'int' to 'llvm::VPValue *'
C:\ws\src\llvm\lib\Transforms\Vectorize\VPlan.cpp(892): note: Conversion from integral type to pointer type requires reinterpret_cast, C-style cast or function-style cast
C:\ws\src\llvm\lib\Transforms\Vectorize\VPlanValue.h(156): note: see declaration of 'llvm::VPValue::replaceAllUsesWith'
```


https://github.com/llvm/llvm-project/pull/142372