Remove `(String, String)` variants of `setProperty()` and `withProperty()` from `MockEnvironment`

[sbrannen]

Overview

Since setProperty(String, Object) and withProperty(String, Object) methods were introduced in MockEnvironment in 6.2.8, we should remove the obsolete variants with (String, String) signatures in 7.0.

Related Issues

• MockEnvironment does not accept Object property values #34947