Clean up unsupported VS versions

[int19h]

There's a bunch of dead code in PTVS that is there solely to support old VS versions that are no longer targeted, and needs to be cleaned up.

For low-hanging fruit, we should look for #if DEV14 and similar checks.

In some cases, it's less obvious - e.g. for mixed-mode, LocalComponent is distinct from LocalStackWalkingComponent solely as a workaround for an old VS bug that has long since been fixed. There might also be cases where code can be simplified significantly by using newer VS APIs that couldn't previously be used.