bundler: remove broad FILES definition

This effectively reverts commit
4e8853ca

 [bundler: Fix QA new Error]

The original QA error is now handled by changes to the ruby.bbclass to
properly handle build_info and extensions directories that Ruby 2.0.0
now creates while installing gems.

This revert isn't specifically required but by removing this broad
definition of FILES the hope is that other ruby recipes won't copy
this behavior which can actually lead to other QA errors/warnings,
depending on what gets installed in the build_info and extensions
directories.

Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>