gh-39114: Remove unnecessary dummy lines in doctests
    
I didn't know the dummy line is unnecessary while working on
#38945 . Better removing it so that
future developers won't stumble upon it in the future.

Side note: ideally instead of `known bug (meson ...)` we could just do
`optional - !meson`.

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### ⌛ Dependencies

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URL: #39114
Reported by: user202729
Reviewer(s): Kwankyu Lee

Author: Release Manager

src/sage/repl/interpreter.py

@@ -75,8 +75,7 @@
 
     sage: from sage.repl.interpreter import get_test_shell
     sage: shell = get_test_shell()
-    sage: print("dummy line"); shell.run_cell('1/0') # known bug (meson doesn't include the Cython source code) # see #25320 for the reason of the `...` and the dummy line in this test
-    dummy line
+    sage: shell.run_cell('1/0') # known bug (meson doesn't include the Cython source code)
     ...
     ZeroDivisionError...Traceback (most recent call last)
     ...

src/sage/repl/ipython_extension.py

@@ -403,14 +403,13 @@ def cython(self, line, cell):
             ....: ''')
             UsageError: unrecognized arguments: --help
 
-        Test invalid quotes (see :mod:`sage.repl.interpreter` for explanation of the dummy line)::
+        Test invalid quotes::
 
             sage: # needs sage.misc.cython
-            sage: print("dummy line"); shell.run_cell('''
+            sage: shell.run_cell('''
             ....: %%cython --a='
             ....: print(1)
             ....: ''')
-            dummy line
             ...
             ValueError...Traceback (most recent call last)
             ...