[lldb] Move comment about noindex next to line it refers to

The comment was originally added in 34769d80. Then D44526
removed the flag added there (but kept the comment), and then
D66966 reintroduced a .noindex dir (which D68606 and then 33fca978
moved around a bit).

No behavior change.

Differential Revision: https://reviews.llvm.org/D107341