Add default implementation for IDocument::fallbackSaveAs(Path|FileName)

The methods are only relevant for documents without a filePath, and
there was a mix of different irrelevant implementations present in
subclasses.

Change-Id: I4f57d306e5ddd913974cfe6ed0b4db062eb907a1
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/plugins/android/androidmanifestdocument.cpp

@@ -59,16 +59,6 @@ bool AndroidManifestDocument::save(QString *errorString, const QString &fileName
     return result;
 }
 
-QString AndroidManifestDocument::fallbackSaveAsPath() const
-{
-    return filePath().toFileInfo().absolutePath();
-}
-
-QString AndroidManifestDocument::fallbackSaveAsFileName() const
-{
-    return filePath().fileName();
-}
-
 bool AndroidManifestDocument::isModified() const
 {
     return TextDocument::isModified() ||  m_editorWidget->isModified();