Make IFile::isReadOnly consistent.

It is supposed to refer to the property of the file on disk (if there is
any).

Task-number: QTCREATORBUG-4998
Change-Id: Iaed62c17d124b364aecec4d1f910046bade42d40
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>

src/plugins/tasklist/taskfile.cpp

@@ -81,11 +81,6 @@ bool TaskFile::isModified() const
     return false;
 }
 
-bool TaskFile::isReadOnly() const
-{
-    return true;
-}
-
 bool TaskFile::isSaveAsAllowed() const
 {
     return false;

src/plugins/tasklist/taskfile.h

@@ -56,7 +56,6 @@ public:
     QString mimeType() const;
 
     bool isModified() const;
-    bool isReadOnly() const;
     bool isSaveAsAllowed() const;
 
     ReloadBehavior reloadBehavior(ChangeTrigger state, ChangeType type) const;