readersearch: do not show regexp checkbutton in pdf (#8450)
readersearch: do not show regexp checkbutton in pdf (#8450)

Minor optimization.
Frenzie/koreader,NiLuJe/koreader,NiLuJe/koreader,poire-z/koreader,koreader/koreader,Frenzie/koreader,koreader/koreader,poire-z/koreader