node tests: Add coverage for clear_search_form.
node tests: Add coverage for clear_search_form.

This is a prep commit to help us soon remove 44 months worth of
bit-rotted code.

zulip/zulip,kou/zulip,rht/zulip,kou/zulip,andersk/zulip,zulip/zulip,rht/zulip,andersk/zulip,rht/zulip,kou/zulip,rht/zulip,zulip/zulip,rht/zulip,rht/zulip,kou/zulip,kou/zulip,rht/zulip,kou/zulip,andersk/zulip,zulip/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip,kou/zulip,zulip/zulip,zulip/zulip,andersk/zulip