[VM] Delete some dead code in gen_snapshot.cc
[VM] Delete some dead code in gen_snapshot.cc

Change-Id: I26428cab1fb6cf9a0bb243716cf483ededd394bc
Reviewed-on: https://dart-review.googlesource.com/76800
Commit-Queue: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>

dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk