DOC: Remove unused concepts page

src/doc/concepts.rst

-========================
-The concepts of pycaosdb
-========================
-
-Some text...
-

src/doc/index.rst

@@ -9,7 +9,6 @@ Welcome to the documentation of LinkAhead's web UI!
 
    Manual installation <install>
    Tutorials <tutorials/index>
-   Concepts <concepts>
    administration/index.rst
    Extending the UI <extension>
    API <api/index>
@@ -19,8 +18,9 @@ Welcome to the documentation of LinkAhead's web UI!
    Go to `demo.indiscale.com <https://demo.indiscale.com>`__ and take the interactive tour to learn
    how to use LinkAhead's web interface.
 
-This documentation helps you to :doc:`install the web UI <install>`, explains the most important
-:doc:`concepts<concepts>` and offers a range of :doc:`tutorials<tutorials/index>`.
+This documentation helps you to :doc:`install the web UI <install>`, explains
+the most important concepts and offers a range of
+:doc:`tutorials<tutorials/index>`.
 
 
 Indices and tables