Avoid printing some redundant name qualifiers in completion

Avoid printing some redundant name qualifiers in completion

Summary:
Adjusted PrintingPolicy inside code completion to avoid printing some
redundant name qualifiers.

Before this change, typedefs that were written unqualified in source
code were printed with qualifiers in completion. For example, in the
following code

    struct foo {
        typedef int type;
        type method();
    };

completion item for `method` had return type of `foo::type`, even
though the original code used `type` without qualifiers.
After this change, the completion item has return type `type`, as
originally written in the source code.

Note that this change does not suppress qualifiers written by the
user. For example, in the following code

    typedef int type;
    struct foo {
        typedef int type;
        ::type method(foo::type);
    };

completion item for `method` has return type of `::type` and
parameter type of `foo::type`, as originally written in the source
code.

Reviewers: arphaman, bkramer, klimek

Reviewed By: arphaman

Subscribers: mgorny, eraman, cfe-commits

Differential Revision: https://reviews.llvm.org/D38538

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@317677 91177308-0d34-0410-b5e6-96231b3b80d8