Add clean step to remove Soong's host copies of libconscrypt_openjdk_jni.so

An ABI incompatible change along with inability to
express the JNI dependency can result in build failures, see
b/170311371#comment8 for how to reproduce.  Tested by using that
repro and verifying this clean step fixes it.  Hopefully the
path being removed is correct for all host platforms.

Fixes: 170311371
Bug: 170389375
Test: As described above
Change-Id: I95ea952bf31d8e9caa8c42d21f2db1968cbe9097