removed important font size declarations from responsive.less

[mnods]

Cannot see any impact with removing these - now makes it easy to override font size for relevant media queries.

[gjb2048]

Hi Mike,

As package-lock.json is not needed, please combine into one commit and resubmit.

Thanks,

Gareth

[gjb2048]

I ask for 'single commits' as that makes it easier for knowing what was done for a single issue and for back-porting with 'cherry-pick'.