[TASK] Drop the example PHPUnit configuration file (#29)

This file has caused more confusion than enlightenment.

.travis.yml

@@ -45,11 +45,6 @@ script:
   echo "Running the unit tests";
   composer ci:tests:unit;
 
-- >
-  echo;
-  echo "Running the model tests";
-  .Build/vendor/bin/phpunit -c Configuration/PHPUnit/ModelTests.xml;
-
 - >
   echo;
   echo "Running the functional tests";

Configuration/PHPUnit/ModelTests.xml

@@ -1,17 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/6.5/phpunit.xsd"
-         backupGlobals="true"
-         bootstrap="../../.Build/vendor/nimut/testing-framework/res/Configuration/UnitTestsBootstrap.php"
-         colors="true"
->
-    <testsuites>
-        <!--
-            There can also be multiple "testsuite" elements, e.g., for executing all unit tests from multiple extensions.
-        -->
-        <testsuite name="Model unit tests">
-            <directory>../../Tests/Unit/Domain/Model</directory>
-        </testsuite>
-    </testsuites>
-</phpunit>

README.md

@@ -64,12 +64,6 @@ In the Run configurations, copy the PHPUnit configuration and use these settings
 - [x] Use alternative configuration file
 - use `.Build/vendor/nimut/testing-framework/res/Configuration/FunctionalTests.xml`
 
-### Example PHPUnit configuration file with a test suite
-
-The file [`Configuration/PHPUnit/ModelTests.xml`](Configuration/PHPUnit/ModelTests.xml)
-contains an example of a PHPUnit configuration file that has a test suite
-(based on the unit tests configuration file from the testing framework).
-
 ## Creating new extensions with automated tests
 
 For creating new extensions, I recommend taking