remove references to RCTDynamicColor

[Saadnajmi]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

In #1028 I removed RCTDynamicColor.h/.m . There was still an explicit reference to the class in our unit tests. I'm not sure why that wasn't caught.

Changelog

[macOS] [Fixed] - Removed reference to RCTDynamicColor in our unit tests.

Test Plan

CI should pass.