Chenged a forgotten `\thesis@@lower{...}` invocation in the definition

of `\thesis@czech@declaration` for the Faculty of Arts into
`\thesis@lower{czech@...}`, so that the macro always expands to the
correct output regardless of the current locale.

This is merely a matter of consistency, since the style file of the
Faculty of Arts only uses Czech strings within the Czech locale.

fithesis3/locale/czech.dtx

@@ -227,7 +227,7 @@
 % Zástupné texty
 \def\thesis@czech@facultyName{Filozofická fakulta}
 \def\thesis@czech@declaration{%
-  Prohlašuji, že jsem \thesis@@lower{typeName@akuzativ}
+  Prohlašuji, že jsem \thesis@lower{czech@typeName@akuzativ}
   vypracoval\thesis@czech@gender@koncovka\ samostatně~s využitím
   uvedené literatury.}