Bug 28522: Correct eslint errors in staff-global.js

Bug 28522: Correct eslint errors in staff-global.js

This patch makes minor corrections to staff-global.js in order to quiet
warnings from ESLint. This includes:

- Remove unused variables
- Declare undeclared variables
- Update list of global and exported variables and functions
- Correct whitespace
- Remove an unused function (paramOfUrl)

To test, apply the patch and clear your browser cache if necessary.

- Confirm that the first search header form field has focus when
  switching bewteen pages.
- Confirm that text entered in any search header form field persists
  when you switch search header form tabs, e.g. a word typed into the
  "Check out" tab is copied to the "Check in" form when you switch to
  that tab.
- Perform a search from the "Search the catalog" tab in the header. On
  the search results page and any following detail page your search term
  should remain in the header search form.
- From a bibliographic detail page, confirm that selecting a list from
  the "Add to list" button menu correctly triggers a popup window.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>