Fix compiling against 3.13.x

https://github.com/flutter/flutter/issues/127606 has been fixed for quite some time and is no longer needed. In addition, the inclusion of https://dart.googlesource.com/tools.git@545d7e1c73ce21b8c91f638021f9d487d324a501 causes 3.13.x to fail with the following error:

output: Error: Couldn't resolve the package 'linter' in 'package:linter/src/rules.dart'. analytics_manager.dart:223:23: Error: The method 'send' isn't defined for the class 'Analytics'.

Remove the inclusion of unified_analytics.