Remove unnecessary TPAC toggle strings on staff client splash page

Accidentally reintroduced with commit ad86ef5d3c689c9b514cc09bfc93e7f451461dc7,
we can skip adding back TPAC toggle strings to the index.xhtml file since that
toggle action has been removed from the page.

Signed-off-by: Ben Shum <bshum@biblio.org>