Removing unused legacy price code

[jonathanKingston]

Description

Removing some legacy code that doesn't ever look used in m2. There don't appear to be ant elements with #price_default in the code. This is one of the many uses of Event.observe which hopefully we can move towards removing.

The code doesn't appear to have tests or any other remaining structure relating to it.

Manual testing scenarios

1. Check anything that would contain prices, however as mentioned I can't see anything that would trigger this code.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)