Fix horizontal scrolling caused by scaling on the subscribe CTA h2

[PaulAdamDavis]

transform: scale(1.15); on the subscribe CTA h2 caused horizontal scrolling on smaller screens, as illustrated by the red outlines in the before screenshot.

This PR removes that transform in favour if increasing the font-size by 15%, matching the same visual size that the transform produced.

Before:

After:

[JohnONolan]

Agree with approach, but if we're going to manually specify font sizes then lets just specify absolute values in rem rather than calc * 1.15 - makes it a bit more readable

[PaulAdamDavis]

Absolute valued was my first approach, but I thought this would make find/replace easier. Agreed though, will change.

[JohnONolan]

@PaulAdamDavis Media query style now specifies EM rather than REM, is that intentional or typo?

[PaulAdamDavis]

@JohnONolan Typo, thanks for spotting! Fixed.