Enabled sending of user properties

[j05u3]

Fix for #309

Tested by checking the chrome debug console:

And the firebase analytics debug console:

Environment in which it was tested:

Dart version: 2.8.0

OS: windows

Flutter doctor just in case:

[√] Flutter (Channel dev, v1.16.1, on Microsoft Windows [Version 10.0.18363.752], locale en-US)
    • Flutter version 1.16.1 at C:\dev\flutter
    • Framework revision e6b0f5f238 (11 days ago), 2020-03-18 21:56:02 -0400
    • Engine revision 216c420a2c
    • Dart version 2.8.0 (build 2.8.0-dev.15.0 96cf889e6b)


[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at C:\dev\android_home
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 29.0.2
    • ANDROID_HOME = C:\dev\android_home
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 3.6)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 44.0.2
    • Dart plugin version 192.7761
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)

[√] VS Code (version 1.43.2)
    • VS Code at C:\Users\josue\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.8.1

[√] Connected device (2 available)
    • Chrome     • chrome     • web-javascript • Google Chrome 80.0.3987.149
    • Web Server • web-server • web-javascript • Flutter Tools

• No issues found!

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[j05u3]

@googlebot I signed it!

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[kevmoo]

Please update the version to 7.2.2 in the pubspec and changelog

...this is kind of a breaking change, since we're changing APIs and deleting classes. But since these bits are unusable, we'll call it fine.

[j05u3]

Please update the version to 7.2.2 in the pubspec and changelog

...this is kind of a breaking change, since we're changing APIs and deleting classes. But since these bits are unusable, we'll call it fine.

Thanks for the review, I just pushed the requested changes