CMakeProjectManager: Remove isCmakeChanged state

Since CMake's file-api cache is the only source of truth for
CMake configuration, there is no need to keep track of such
a state.

Qt Creator will issue -D<var>=<value> -U<var> command line
parameters for CMake, which will update the file api json files.

Change-Id: I08e7041a95422549502eb7961f96570225e942fa
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildconfiguration.cpp

@@ -526,8 +526,7 @@ void CMakeBuildSettingsWidget::updateButtonState()
             });
 
     m_resetButton->setEnabled(m_configModel->hasChanges() && !isParsing);
-    m_reconfigureButton->setEnabled((!configChanges.isEmpty() || m_configModel->hasCMakeChanges())
-                                    && !isParsing);
+    m_reconfigureButton->setEnabled(!configChanges.isEmpty() && !isParsing);
     m_buildConfiguration->setConfigurationChanges(configChanges);
 }