Revert "[libc++] Add test_iterators.h to the modulemap (#181351)"

This reverts commit 04ef765b65040e1df4cafaf3dacc26fa5d48e519.

This was causing buildbot failures for premerge:
1. https://lab.llvm.org/staging/#/builders/192/builds/20135

GitOrigin-RevId: ab88d9af5371ef62a636fc780c88cf6d3487c584