Remove potentially dead code from make_simplified_union

[hauntsaninja]

I was looking into optimising a couple code paths. This change is likely incorrect, but unit tests seemed to pass for me locally without this. We should have a test that covers this and hopefully primer reveals one.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

mypy (https://github.com/python/mypy)
+ mypy/checker.py:1389: error: Left operand of "or" is always false  [redundant-expr]

pytest (https://github.com/pytest-dev/pytest)
+ src/_pytest/config/findpaths.py:217: error: Right operand of "or" is never evaluated  [unreachable]

Tanjun (https://github.com/FasterSpeeding/Tanjun)
+ tanjun/commands/slash.py:808: error: Statement is unreachable  [unreachable]

dragonchain (https://github.com/dragonchain/dragonchain)
+ dragonchain/transaction_processor/level_4_actions.py:119:5: error: Need type annotation for "validations" (hint: "validations: List[<type>] = ...")  [var-annotated]

cwltool (https://github.com/common-workflow-language/cwltool)
+ cwltool/update.py: note: In function "checkversion":
+ cwltool/update.py:277:5: error: Statement is unreachable  [unreachable]

rich (https://github.com/Textualize/rich)
+ rich/table.py:666: error: Right operand of "or" is never evaluated  [unreachable]
+ rich/table.py:674: error: Right operand of "or" is never evaluated  [unreachable]
+ rich/style.py:713: error: If condition is always true  [redundant-expr]

streamlit (https://github.com/streamlit/streamlit)
+ lib/streamlit/runtime/runtime.py: note: In member "connect_session" of class "Runtime":
+ lib/streamlit/runtime/runtime.py:368:82: error: Right operand of "or" is never evaluated  [unreachable]