Bump versions of agp and robolectric, and configure to use SDK 35

[gmackall]

Bumps the version of AGP used in the IDE-support build.gradle, as well as the robolectric version in both the IDE-support build.gradle and test-runner-build.gradle.

This is the current latest robolectric: https://github.com/robolectric/robolectric/releases/tag/robolectric-4.14.1.

Also

1. configures robolectric to use API 35, and
2. removes the use of a deprecated class which (from what I could tell) looked like it was just used for setup, and the test still passes without it.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or the PR is test-exempt. See testing the engine for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[gmackall]

cc @utzcoz, just because I've seen you make robolectric related contributions here (no actions needed but any thoughts welcome!)

[utzcoz]

@gmackall Thanks for your ping. Yeah. I have updated Robolectric version for flutter/engine multiple times. This PR looks great to me. Sorry, but I don't have permission to approve it for you.