populate metadata - remove try/except

[will-moore]

Fixes #189.

This removes the annoying extra exception from script logs by explicitly checking whether we are using old or recent metadata plugin, instead of just try/except.

To test:

• Run populate_metadata script with a valid (working) csv OR with an invalid csv (e.g. has string in a number column)
• The error logs shouldn't contain:

  File "./script", line 124, in populate_metadata
    ctx.parse_from_handle(data)
AttributeError: 'ParsingContext' object has no attribute 'parse_from_handle'

[dominikl]

👍 Looks good. Didn't get the error log.