refactor: Removed obsolete copyResource function

[breautek]

Platforms affected

Android

Motivation and Context

Removes a copied/pasted function in accordance to it's TODO. The pasted copyResource function appeared to be a stopgap measure to address a bug that appeared pre cordova-android@4. The note said to remove the function and bring the required cordova-android engine to >= 4.0.0

The plugin currently requires cordova-android >= 6.3.0 so no changes there was required.

Description

Deleted local copy of copyResource and replaced usages with CordovaResourceApi version.

Testing

ran npm test and manually used copyTo api.

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary