static/frontend/search: update no results message for indentifier search
static/frontend/search: update no results message for indentifier search

For golang/go#44142

Change-Id: Ic47f3aff429f11dfadeaa5926bc9f78bf152303b
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/336289
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite