[clangd] Skip informative qualifier chunks.

Summary:
Completion results look much nicer without them.
Informative qualifiers are stored for every method from a base class, even when
calling those methods does not require any qualifiers. For example,
    struct Foo { int foo(); };
    struct Bar : Foo { };
    void test() { Bar(). // Completion item label was 'Foo::foo' before,
                         // but inserted text was simply 'foo'.
                         // We now simply show 'foo' in completion item label.

They effectively cluttered the completion list without providing much value.

Reviewers: bkramer, krasimir, rwols

Reviewed By: rwols

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D38083

llvm-svn: 314445