(calc-init-extensions): Remove old code.

(calc-init-extensions):  Remove old code.

(math-expr-data, math-mt-many, math-mt-func, calc-z-prefix-buf)
(calc-z-prefix-msgs):  New variables.

(calc-z-prefix-help, calc-user-function-list):  Use declared variables
calc-z-prefix-buf, calc-z-prefix-msgs.

(math-normalize-nonstandard):  Use declared variable math-normalize-a.

(math-map-tree, math-map-tree-rec):  Use declared variables
math-mt-many, math-mt-func.

(math-read-expression, math-read-string):  Use declared variable math-expr-data.