[TASK] Remove additional Fluid links (TYPO3-Documentation#1974)

In the Introduction page, there was an additional section with
links to external sources. This is now mostly redundant, as
more information has been included in the Fluid chapter. For
example the page "Syntax" was included, so it is no longer
necessary to link to external source. Also, some of the links
are duplicates with the links already included on the page
"Using Fluid in TYPO3".

Related: TYPO3-Documentation/TYPO3CMS-Book-ExtbaseFluid#536

Documentation/ApiOverview/Fluid/Introduction.rst

@@ -7,13 +7,13 @@ Introduction to Fluid
 =====================
 
 Fluid is TYPO3’s default rendering engine but can also be used in standalone PHP projects.
-The `Fluid source code <https://github.com/TYPO3/Fluid>`__ is being developed as an 
+The `Fluid source code <https://github.com/TYPO3/Fluid>`__ is being developed as an
 independent project outside of the TYPO3 Core.
 
-Fluid is based on XML and you can use HTML markup in Fluid. 
+Fluid is based on XML and you can use HTML markup in Fluid.
 
-Fluid ViewHelpers can be used for various purposes. Some transform data, some include 
-Partials, some loop over data or even set variables. You can find a complete list of 
+Fluid ViewHelpers can be used for various purposes. Some transform data, some include
+Partials, some loop over data or even set variables. You can find a complete list of
 them in the :ref:`ViewHelper Reference <t3viewhelper:start>`.
 
 You can :ref:`write your own custom ViewHelper <fluid-custom-viewhelper>`,
@@ -308,28 +308,3 @@ Set the Fluid paths with TypoScript using :ref:`t3tsref:cobj-fluidtemplate`
          <p> some text </p>
       </div>
    </div>
-
-
-
-Further information
-===================
-
-To get an introduction to the basics of Fluid:
-
-* `The Fluid Syntax <https://github.com/TYPO3/Fluid/blob/master/doc/FLUID_SYNTAX.md>`__
-* `ViewHelpers - what these classes do in the Fluid language <https://github.com/TYPO3/Fluid/blob/master/doc/FLUID_VIEWHELPERS.md>`__
-
-You may want to follow one of these comprehensive
-tutorials:
-
-* :doc:`t3sitepackage:Index` which shows you how to create a theme for your site
-  using Fluid.
-* :ref:`Create custom content elements <adding-your-own-content-elements>`
-* :doc:`t3extbasebook:Index`
-* Use Fluid to create emails using the :ref:`TYPO3 Mail API <mail-fluid-email>`
-
-Once you have successfully completed your fist steps, these references might come
-in handy:
-
-* `24 TIPS & TRICKS FOR FLUID <https://usetypo3.com/24-fluid-tips.html>`__
-* :doc:`Fluid Viewhelper Reference <t3viewhelper:Index>`