Revert "[lldb][cmake] Also use local submodule visibility on Darwin"

This reverts commit 8baa0b94. This broke the
LLDB Green Dragon bot where htonl is getting miscompiled on macOS 10.14 and 10.15
SDKs, causing networking tests to fail as IP addressed were being inverted
(e.g., 127.0.0.1 became 1.0.0.127 with an enabled modules build).

Reverting until this is fixed.