Fix phase banner left/right spacing on some pages

[andysellick]

⚠️ This repo is Continuously Deployed: make sure you follow the guidance ⚠️

What

Fixes a problem with unneeded left/right padding around the phase banner.

• below the tablet breakpoint (around 1020px) the phase banner at the top of some pages was being padded left and right, which indented it from the rest of the page
• caused by the govuk-frontend grid wrapping classes, which were unnecessary
• some wrapping divs moved instead to support the phase label, which is similar but does require additional wrapping elements
• also remove some unnecessary logic

Example pages:

• https://www.gov.uk/hmrc-internal-manuals/air-passenger-duty/updates (phase banner with problem)
• https://www.gov.uk/service-manual (phase label, should be unaffected)
• https://www.gov.uk/world/organisations/british-consulate-general-barcelona/office/british-consulate-general-barcelona (also rendered by government-frontend, no phase banner or phase label, should be unaffected)

Why

Visual changes

Desktop - no change.

Tablet - change:

Before	After

Mobile - change:

Before	After