(PUP-3282) Remove support for method access to variables in ERB templ.

This removes the deprecated support to produce lookup of variable
names when a missing method was invoked having the same name as
the variable.

This is now an error, just like calling any other missing method.
Merge pull request #3358 from hlindberg/PUP-3282_remove_erb-method-attributes

(PUP-3282) Remove support for method access to variables in ERB templ.