Update date of birth - move h1 inside legend
Update date of birth - move h1 inside legend

This removes the duplication of the h1 and legend text.

gavinwye/govuk_prototype_kit,dwpdigitaltech/hrt-prototype,joelanman/govuk_prototype_kit,benjeffreys/hmcts-idam-proto,joelanman/govuk_prototype_kit,alphagov/govuk_prototype_kit,alphagov/govuk_prototype_kit,alphagov/govuk_prototype_kit,dwpdigitaltech/hrt-prototype,benjeffreys/hmcts-idam-proto,joelanman/govuk_prototype_kit,benjeffreys/hmcts-idam-proto,dwpdigitaltech/hrt-prototype,gavinwye/govuk_prototype_kit