Getting entries related to current entries categories
This solution should also remove your "featured" category entries:

{% set categories = craft.categories.relatedTo(entry) %}
{% set featuredCategory = craft.categories.slug('featured').first() %}

{% set allIds = [] %}
{% for id in categories.ids() if id != featuredCategory.id %}
    {% set allIds = allIds|merge([id]) %}
{% endfor %}

{% set entries = craft.entries.relatedTo(allIds) %}