cmPolicies: Remove now-unused REQUIRED_IF_USED and REQUIRED_ALWAYS states

Source/cmAddCustomCommandCommand.cxx

Source/cmAddLibraryCommand.cxx

Source/cmBreakCommand.cxx

Source/cmCMakePolicyCommand.cxx

Source/cmComputeLinkDepends.cxx

Source/cmComputeLinkInformation.cxx

Source/cmComputeTargetDepends.cxx

Source/cmConditionEvaluator.cxx

Source/cmCoreTryCompile.cxx

Source/cmDebuggerVariablesHelper.cxx

Source/cmExportCommand.cxx

Source/cmExportInstallFileGenerator.cxx

Source/cmFileCommand.cxx

Source/cmFindPackageCommand.cxx

Source/cmFindProgramCommand.cxx

Source/cmGeneratorExpressionEvaluationFile.cxx

Source/cmGeneratorExpressionNode.cxx

Source/cmGeneratorTarget.cxx

Source/cmGeneratorTarget_IncludeDirectories.cxx

Source/cmGeneratorTarget_Link.cxx