[nit] remove useless --' test comments (#20394)

0d61fd0
and
94745f5
seem to have added these useless --' comments by mistake in the course
of doing other things.

Author: wyattscarpenter

test-data/unit/check-incremental.test

@@ -2336,7 +2336,6 @@ tmp/c.py:1: error: Module "d" has no attribute "x"
 [out]
 [out2]
 mypy: can't read file 'tmp/nonexistent.py': No such file or directory
--- '
 
 [case testSerializeAbstractPropertyIncremental]
 from abc import abstractmethod

test-data/unit/cmdline.test

@@ -117,7 +117,6 @@ sub.pkg is not a valid Python package name
 mypy: can't decode file 'a.py': unknown encoding: uft-8
 == Return code: 2
 
--- '
 [case testCannotIgnoreDuplicateModule]
 # cmd: mypy one/mod/__init__.py two/mod/__init__.py
 [file one/mod/__init__.py]
@@ -546,7 +545,6 @@ a/b/c/d/e/__init__.py:3: error: Argument 1 to "g" has incompatible type "None";
 [out]
 mypy: can't read file 'nope.py': No such file or directory
 == Return code: 2
---'
 
 [case testModulesAndPackages]
 # cmd: mypy --package p.a --package p.b --module c