Remove mention of requirements.in from 735

This is extending the PEP text for an ancillary point of confusion --
there are tool users for `uv` (and possibly `pip-tools`) who do not
understand that `requirements.in` is a convention that does not
represent a significantly distinct file-format.

Discussing the difference between these only lengthens the already
very-long PEP text, and does not add value vis-a-vis community
standards. Given that neither `requirements.in` nor `requirements.txt`
have clear specifications, other than "what `pip` accepts", keeping
with the older and more standardized naming keeps things shorter and
simpler.

peps/pep-0735.rst

@@ -570,21 +570,6 @@ defined dynamically. Requirements loaded from ``requirements.txt`` files and
 definitions of static lists prior to ``setup()`` invocation readily analogize
 with Dependency Groups.
 
-requirements.txt vs requirements.in
------------------------------------
-
-Using tools such as ``pip-tools``'s ``pip-compile`` or ``poetry``'s
-``poetry export``, many users produce ``requirements.txt`` files which contain
-*locked* requirements data, with exact versions and hashes pinned for an entire
-environment.
-
-A community standard which is promoted in several projects' documentation,
-including that of ``pip-tools``, has evolved of calling the input (unlocked)
-requirements data ``requirements.in`` and the locked data ``requirements.txt``.
-
-Users familiar with this usage should typically think of Dependency Groups as
-their ``requirements.in`` data, not their locked dependency data.
-
 Interfaces for Use of Dependency Groups
 ---------------------------------------