Remove unused using declarations in `CLI/Generator.cs`.
Remove unused using declarations in `CLI/Generator.cs`.

zillemarco/CppSharp,ddobrev/CppSharp,mono/CppSharp,mono/CppSharp,zillemarco/CppSharp,zillemarco/CppSharp,ddobrev/CppSharp,zillemarco/CppSharp,zillemarco/CppSharp,mono/CppSharp,ddobrev/CppSharp,mono/CppSharp,ddobrev/CppSharp,mono/CppSharp,ddobrev/CppSharp,mono/CppSharp