Tests/RunCMake: Update cmake_minimum_required versions

For policy-specific tests, use the version before the policy was
introduced.  Otherwise, use 3.5 where possible.

Also, remove `cmake_minimum_required()` and `project()` calls from
individual cases where they are handled by `CMakeLists.txt`.

Tests/RunCMake/XcodeProject/XcodeSchemaProperty.cmake

@@ -1,9 +1,7 @@
-cmake_minimum_required(VERSION 3.7)
+enable_language(CXX)
 
 set(CMAKE_XCODE_GENERATE_SCHEME ON)
 
-project(XcodeSchemaProperty CXX)
-
 function(create_scheme_for_variable variable)
   set(CMAKE_XCODE_SCHEME_${variable} ON)
   add_executable(${variable} main.cpp)