rm '== false' from boolean expressions (advised by clang-tidy)

.clang-tidy

Tests/UnitTests/GUI/TestComponentProxyModel.cpp

Tests/UnitTests/GUI/TestExternalProperty.cpp

Tests/UnitTests/GUI/TestMapperCases.cpp

Tests/UnitTests/GUI/TestMaterialModel.cpp

Tests/UnitTests/GUI/TestMaterialPropertyController.cpp

Tests/UnitTests/GUI/TestOutputDataIOService.cpp

Tests/UnitTests/GUI/TestParticleItem.cpp

Tests/UnitTests/GUI/TestProjectDocument.cpp

Tests/UnitTests/GUI/TestProjectUtils.cpp

Tests/UnitTests/GUI/TestProxyModelStrategy.cpp

Tests/UnitTests/GUI/TestSessionItem.cpp