MDL-45336 questionbank: use core strings instead of quiz

AMOS BEGIN
 CPY [categories,mod_quiz],[categories,question]
 CPY [unusedcategorydeleted,mod_quiz],[unusedcategorydeleted,question]
 CPY [export,mod_quiz],[export,core_question]
 CPY [import,mod_quiz],[import,core_question]
AMOS END
MDL-45336 lesson: copied used strings from quiz

AMOS BEGIN
 CPY [false,mod_quiz],[false,mod_lesson]
 CPY [fractionsaddwrong,mod_quiz],[fractionsaddwrong,mod_lesson]
 CPY [fractionsnomax,mod_quiz],[fractionsnomax,mod_lesson]
 CPY [notenoughsubquestions,mod_quiz],[notenoughsubquestions,mod_lesson]
 CPY [true,mod_quiz],[true,mod_lesson]
AMOS END