Revert "2020-04-29 Sterling Augustine <saugustine@google.com>"

Revert "2020-04-29  Sterling Augustine <saugustine@google.com>"

This reverts commit 84ed7a472551bce1ac58e0eced619433fabc956c.

The problem that the commit attempts to address has already been fixed in
commit 770479f223e "gdb: Fix toplevel types with -fdebug-types-section".

The commit itself is superfluous because it sets list_in_scope at a point that
it's already set (by start_symtab).