[lldb][test_suite] skip tests of `libstdcpp` on Android and clean up

Summary: Delete the android target from `libstdcpp` test category, since android no longer support libstdcxx

Reviewers: xiaobai, labath

Reviewed By: labath

Subscribers: srhines, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D64771

llvm-svn: 366770