Revert "Emit DW_AT_object_pointer once, on the declaration, for each function."

Breaks GDB buildbot
(http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/14517)

GCC emits DW_AT_object_pointer /everywhere/ (declaration, abstract
definition, inlined subroutine), but it looks like GCC relies on it
being somewhere other than the declaration, at least. I'll experiment
further & can hopefully still remove it from the inlined_subroutine.

This reverts commit r207705.

llvm-svn: 207719