Remove unused variables from previously-shared function

[eileenmcnaughton]

The buildMembershipBlock function was unshared by @mattwire a while ago due to the usual business of cramming all sorts of unshared stuff into a shared function. Per the code comments follow on cleanup was required to get rid of the cruft not relevant to all 3 forms.

In particular a lot of it is only relevant to the Main form - which has the input fields. This removes some variables from the other two

• $radioOptAttrs is set & unuset but never used - this makes sense as the point of it is to about adding options to a field on the Main contribution page - which no longer shares this function.

• $radio is set & unset but never used

• $allowAutoRenewMembership is set but never used

• $javascriptMethod is set but only used to add to $radioOptAttrs

[civibot]

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