Fix text size rendering issue on policy group pages

The overly broad CSS rule was targetting the first child p of any element, eg, LI, ADDRESS, etc. Causing
large text all over the shop. Regardless having chatted to a designer, the make-first-p behaviour is no longer required
anyway, so remove it
Merge pull request #1529 from alphagov/fix-text-size-on-policy-groups

Fix text size rendering issue on policy group pages