Hide vmservice.cc behind PRODUCT macro.
Hide vmservice.cc behind PRODUCT macro.

This removes vmservice.cc from the flutter engine release binary, which saves a few kB.

Tested using tools/test.py in product mode. Verified the binary savings using run_binary_size_analysis.py

Bug: https://github.com/dart-lang/sdk/issues/34895
Change-Id: I74d50d3e177842310e488072f35bc11d1c597036
Reviewed-on: https://dart-review.googlesource.com/c/84683
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>
Commit-Queue: Liam Appelbe <78c2029e58e395825ba7228e218c841bb436a9e9@google.com>

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