Remove old workaround for unloading unversioned soinfo

This code path is/was a workaround for poorly-behaved apps. AFAIK it isn't
needed anymore.

The (needed != nullptr) condition should have been (needed == nullptr), so
rather than unload a library, it tends to do nothing instead. If it can't
find the library, it would segfault.

Bug: http://b/112154263
Test: /data/nativetest/bionic-unit-tests/bionic-unit-tests
Test: /data/nativetest/linker-unit-tests/linker-unit-tests32
Test: apply patch to pi-dev, verify that apps from b/72143978 still work
Change-Id: Ic598cb3dcead9f88005764a9b8746ed6b35f5f38