[analyzer] Don't delete TaintConfig copy constructor

Summary:
Explicitly deleting the copy constructor makes compiling the function
`ento::registerGenericTaintChecker` difficult with some compilers. When we
construct an `llvm::Optional<TaintConfig>`, the optional is constructed with a
const TaintConfig reference which it then uses to invoke the deleted TaintConfig
copy constructor.

I've observered this failing with clang 3.8 on Ubuntu 16.04.

Reviewers: compnerd, Szelethus, boga95, NoQ, alexshap

Subscribers: xazax.hun, baloghadamsoftware, szepet, a.sidorin, mikhail.ramalho, donat.nagy, dkrupp, Charusso, llvm-commits, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66192

llvm-svn: 368779