Revert "Syntax: Test files only need to start with 'syntax_test'"

This reverts commit 644b333.
Closes #405.

Author: FichteFoll

plugins/syntaxtest_dev.py

@@ -95,7 +95,7 @@ def on_modified_async(self):
         """
 
         name = self.view.file_name()
-        if name and not path.basename(name).startswith('syntax_test'):
+        if name and not path.basename(name).startswith('syntax_test_'):
             self.header = None
             return
         self.header = get_syntax_test_tokens(self.view)