Tests: get rid of classes in test files.

Class usage came from the unittest framework and it was always redundant
after migration to the pytest.  This commit removes classes from files
containing tests to make them more readable and understandable.

test/unit/applications/lang/perl.py

@@ -1,9 +1,10 @@
-from unit.applications.proto import TestApplicationProto
+from unit.applications.proto import ApplicationProto
 from unit.option import option
 
 
-class TestApplicationPerl(TestApplicationProto):
-    application_type = "perl"
+class ApplicationPerl(ApplicationProto):
+    def __init__(self, application_type='perl'):
+        self.application_type = application_type
 
     def load(self, script, name='psgi.pl', **kwargs):
         script_path = f'{option.test_dir}/perl/{script}'