refactor($parse): clean up evaled function

[kseamon]

refactor($parse): clean up evaled function

Remove unused variables from the created function.
Use == null instead of (=== null || === undefined)
Don't wrap the evaled function in a closure when not unwrapping promises.
This change also brings a slight performance improvement: http://jsperf.com/optimizing-parse

[mary-poppins]

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[petebacondarwin]

@kseamon - there should be no capital letter at the start of the commit message subject.

[IgorMinar]

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[kseamon]

This PR is obsoleted by #5359