[VM] Remove assert that causes --disassemble-stubs to fail
[VM] Remove assert that causes --disassemble-stubs to fail

R=ma35dd5b79fac84b2bb3b026a16b8becc55af5961@google.com

Using the --disassemble-stubs option on Debug builds of IA32
has been broken for some time (months). This lets it run.
Manually verified that it is correctly printing "this stub"
now.
Bug:
Change-Id: Ieedc17a7141c0c4d8dc1c002882ffd92fdce251d
Reviewed-on: https://dart-review.googlesource.com/23801
Reviewed-by: Martin Kustermann <a35dd5b79fac84b2bb3b026a16b8becc55af5961@google.com>
Commit-Queue: Erik Corry <b520ba1e7f871f909b0b4a9e1cf9a391adc0e954@google.com>

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