Remove definition of ~PlatformNetBSD(), since its declaration is marked as '= default'

Summary: Local definition of ~PlatformNetBSD() results with a compiler error.

Patch by Kamil Rytarowski. Thanks!

Reviewers: joerg, brucem

Subscribers: brucem, lldb-commits

Differential Revision: http://reviews.llvm.org/D13707

llvm-svn: 250249