[libc++] Remove workarounds for re-defining _LIBCPP_ASSERT in the test suite

As a fly-by fix, enable the complexity-changing assertions in __debug_less
only when the full debug mode is enabled, since debugging level 0 is usually
understood to only contain basic assertions that do not change the complexity
of algorithms.

Differential Revision: https://reviews.llvm.org/D121129

NOKEYCHECK=True
GitOrigin-RevId: 95c0f2d115e29e3429226cccc1209f5640dd1b6a
diff --git a/docs/DesignDocs/DebugMode.rst b/docs/DesignDocs/DebugMode.rst
index faf7b8e..b792251 100644
--- a/docs/DesignDocs/DebugMode.rst
+++ b/docs/DesignDocs/DebugMode.rst
@@ -27,18 +27,13 @@
 When ``_LIBCPP_DEBUG`` is not defined, there are no debugging checks performed by
 the library. This is the default.
 
-Basic checks (``_LIBCPP_DEBUG == 0``)
--------------------------------------
-When ``_LIBCPP_DEBUG`` is defined to ``0`` (to be understood as level ``0``), some
-debugging checks are enabled. The non-exhaustive list of things is:
-
-- Many algorithms, such as ``binary_search``, ``merge``, ``next_permutation``, and ``sort``,
-  wrap the user-provided comparator to assert that `!comp(y, x)` whenever
-  `comp(x, y)`. This can cause the user-provided comparator to be evaluated
-  up to twice as many times as it would be without ``_LIBCPP_DEBUG``, and
-  causes the library to violate some of the Standard's complexity clauses.
-
-- FIXME: Update this list
+Comparator consistency checks (``_LIBCPP_DEBUG == 1``)
+------------------------------------------------------
+Libc++ provides some checks for the consistency of comparators passed to algorithms. Specifically,
+many algorithms such as ``binary_search``, ``merge``, ``next_permutation``, and ``sort``, wrap the
+user-provided comparator to assert that `!comp(y, x)` whenever `comp(x, y)`. This can cause the
+user-provided comparator to be evaluated up to twice as many times as it would be without the
+debug mode, and causes the library to violate some of the Standard's complexity clauses.
 
 Iterator debugging checks (``_LIBCPP_DEBUG == 1``)
 --------------------------------------------------