[REF] Replace ->assign with CRM_Core_Smarty::singleton()->assign in preparation for making function shareable

[eileenmcnaughton]

Overview

Minor function change preparatory to other changes - no impact

Before

no change

After

no change

Technical Details

Per PR 1330 there is an intention to make this form receipting function a shared function. Part of making it sharable is making it static.

This is a preparatory refactor towards that end, getting rid of the 'this' in assigning variables to smarty

Comments

@jitendrapurohit just spinning off this small change - we should be able to avoid calling assignMessageVariables which should be deprecated

[civibot]

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[seamuslee001]

@eileenmcnaughton whilst this seems fine i would be more comfortable with a unit test to ensure these variables are indeed assigned right.

[eileenmcnaughton]

@seamuslee001 I think @jitendrapurohit has written a unit test, although it can't be added until we are further along the refactor

[seamuslee001]

Discussed this a bit more with Eileen adn i am satisfied this should be ok merging