compat: remove glibcxx sanity checks

These checks were added in #4339, (see also #4081), to test
our back-compat stubs, however, those stubs no-longer exist (#22930),
meaning that these checks are now just testing some specific standard
library behaviour, without a particular rationale, or reason, compared
to any other standard library functions we use.

There has also been some discussion about the sanity checks in the
context of the libbitcoinkernel refactoring, see
https://github.com/bitcoin/bitcoin/pull/25065#discussion_r880668218.
Removing the checks removes the need to worry about atleast the glibcxx
checks.

Also remove the list of check from the doc in init.h, because it is
incomplete, and anyone who wants to know what checks are included can
look at the function.

src/test/sanity_tests.cpp

@@ -2,7 +2,6 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <compat/sanity.h>
 #include <key.h>
 #include <test/util/setup_common.h>
 #include <util/time.h>
@@ -13,7 +12,6 @@ BOOST_FIXTURE_TEST_SUITE(sanity_tests, BasicTestingSetup)
 
 BOOST_AUTO_TEST_CASE(basic_sanity)
 {
-  BOOST_CHECK_MESSAGE(glibcxx_sanity_test() == true, "stdlib sanity test");
   BOOST_CHECK_MESSAGE(ECC_InitSanityCheck() == true, "secp256k1 sanity test");
   BOOST_CHECK_MESSAGE(ChronoSanityCheck() == true, "chrono epoch test");
 }