test: posix: c_lib_ext: reduce memory requirements for testsuite

Previously, these tests were part of tests/posix/common.
In an effort to tie feature tests to specific POSIX features
(Option Groups), these tests were moved to a separate suite in a
previous commit.

However, the memory requirements for the legacy
tests/posix/common testsuite were significantly higher while the
memory requirements for tests in tests/posix/c_lib_ext are
significantly lower.

Remove the minimum flash and ram requirements to run the test so
that it passes tests on the integration platform qemu_cortex_m0.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>