Remove an unused var in DEPS
Remove an unused var in DEPS

This specific tag for source_maps is not referenced anywhere else.

R=1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com

Change-Id: I7661f60b7263a280ee410741f38a5099912cc2bb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/241360
Auto-Submit: Nate Bosch <dc212c74d8afde9c690fdd09e74d3e5c5d5a3de0@google.com>
Reviewed-by: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>
Commit-Queue: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk