Fixing 'About iNaturalist' links in mobile site

There were 2 problems here. First the about_inaturalist i18n messages
for en and es-MX were missing the % characters; second the messages
were redundant with the about_x messages anyway, just with a different
parameter name. I removed the about_inaturalist i18n messages (rather
than fixing them) and just used the about_x messages instead. I haven't
actually tested this code, so please test to make sure it works as
expected.