For latex at least I think the thing to do is amend tulmtt.fd in base
so that it has
\DeclareFontFamily{TU}{lmtt}{%
\hyphenchar \font\m@ne
\fontdimen3\font\z@%<<
\fontdimen4\font\z@%<<
}
with the two extra lines ensuring that these two font dimens are set to 0.
(If you try this with a latex 2017/01/01 release you need to remake
the format as it is input during format creation)
David
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