[dart2js] Remove unused compile_time_constants.dart.
[dart2js] Remove unused compile_time_constants.dart.

Change-Id: I4a574ac615aabaf63d7bf3e241fc969766f03cf8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/232030
Reviewed-by: Mayank Patke <e0355b78204b67a55a952941c68c8f1b40235938@google.com>
Commit-Queue: Joshua Litt <9f8daed1ab51574c9a48ffacb03e4a1adb4f880c@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