[demangler] No need to space adjacent template closings

With the demangler parenthesizing 'a >> b' inside template parameters,
because C++11 parsing of >> there, we don't really need to add spaces
between adjacent template arg closing '>' chars.  In 2022, that just
looks odd.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D123134