Python: Remove duplicated SSTI tests

Besides the Cheetah tests, which were missing from the query tests.

Author: RasmusWL

python/ql/test/experimental/query-tests/Security/CWE-074-TemplateInjection/CheetahSinks.py

@@ -0,0 +1,22 @@
+from flask import Flask, request
+from Cheetah.Template import Template
+
+
+app = Flask(__name__)
+
+
+@app.route('/other')
+def a():
+    template = request.args.get('template')
+    return Template(template)
+
+
+class Template3(Template):
+    title = 'Hello World Example!'
+    contents = 'Hello World!'
+
+
+@app.route('/other2')
+def b():
+    template = request.args.get('template')
+    t3 = Template3(template)