[analyzer] Deprecate the unused 'analyzer-opt-analyze-nested-blocks' cc1 flag

This flag was introduced by
https://github.com/llvm/llvm-project/commit/6818991d7165f68fe196922d9e5c6648dd57cc47
    commit 6818991d
    Author: Ted Kremenek <kremenek@apple.com>
    Date:   Mon Dec 7 22:06:12 2009 +0000

  Add clang-cc option '-analyzer-opt-analyze-nested-blocks' to treat
  block literals as an entry point for analyzer checks.

The last reference was removed by this commit:
https://github.com/llvm/llvm-project/commit/5c32dfc5fb1cfcff8ae3671284e17daa8da3a188

    commit 5c32dfc5
    Author: Anna Zaks <ganna@apple.com>
    Date:   Fri Dec 21 01:19:15 2012 +0000

  [analyzer] Add blocks and ObjC messages to the call graph.
  This paves the road for constructing a better function dependency graph.
  If we analyze a function before the functions it calls and inlines,
  there is more opportunity for optimization.
  Note, we add call edges to the called m...