ProjectExplorer: Replace the fromMap error return value

... by some out-of-band mechanism, keeping previous functionality.

The driving reason is to get the same fromMap signature as in the
AspectContainer base, however, the whole mechanism seems rather useless:
There are only a few places that actually ever could report errors,
in those places "moving on" looks ok, too, and these few places
are not conceptually different than a lot others.

Removal of this (new) mechanism is left for later.

Change-Id: Ibe7a0456bc3b84a84e942231f14446e783372d76
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildconfiguration.cpp

@@ -1562,16 +1562,6 @@ CMakeBuildConfiguration::~CMakeBuildConfiguration()
     delete m_buildSystem;
 }
 
-void CMakeBuildConfiguration::toMap(QVariantMap &map) const
-{
-    BuildConfiguration::toMap(map);
-}
-
-bool CMakeBuildConfiguration::fromMap(const QVariantMap &map)
-{
-    return BuildConfiguration::fromMap(map);
-}
-
 FilePath CMakeBuildConfiguration::shadowBuildDirectory(const FilePath &projectFilePath,
                                                        const Kit *k,
                                                        const QString &bcName,