doc/doxygen: remove default value for search form

[mguetschow]

Contribution description

The search input field on doc.riot-os-org is prefilled with value="Search", instead of only using the HTML placeholder attribute. I think this was not the case until some recent doxygen version bump, but I am not sure since the corresponding JS-code has been part of the repo for seven years.

Testing procedure

Open https://doc.riot-os.org on Firefox or Chrome, see that the search field is prefilled.

Compare to the CI generated doxygen, which should only use "Search" as placeholder value: https://ci.riot-os.org/results/534d783017ac45f0a2d217c67b876c9f/doc-preview/

Issues/PRs references

Pinging @miri64 as the original author of the js-code.

[riot-ci]

Murdock results

✔️ PASSED

154e0bd doc/doxygen: remove default value for search form

Success	Failures	Total	Runtime
1	0	1	01m:07s

Artifacts

• Documentation preview

[miri64]

LGTM. Why the value was set, I am not sure anymore. As you said, I implemented this 7 years ago and did not touch it much. Most likely, there was some faulty behavior in Doxygen's HTML output.

[mguetschow]

Thanks!