Fix register sentense string

See https://framacolibri.org/t/sinscrire-sur-mobilizon-affiche-au-lieu-du-nom-de-linstance/9838

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/i18n/en_US.json

@@ -277,7 +277,6 @@
   "Published events with <b>{comments}</b> comments and <b>{participations}</b> confirmed participations": "Published events with <b>{comments}</b> comments and <b>{participations}</b> confirmed participations",
   "RSS/Atom Feed": "RSS/Atom Feed",
   "Region": "Region",
-  "Register an account on Mobilizon!": "Register an account on Mobilizon!",
   "Registration is allowed, anyone can register.": "Registration is allowed, anyone can register.",
   "Registration is closed.": "Registration is closed.",
   "Registration is currently closed.": "Registration is currently closed.",

js/src/i18n/fr_FR.json

@@ -563,7 +563,6 @@
   "Refresh profile": "Rafraîchir le profil",
   "Region": "Région",
   "Register": "S'inscrire",
-  "Register an account on Mobilizon!": "S'inscrire sur Mobilizon !",
   "Register an account on {instanceName}!": "S'inscrire sur {instanceName} !",
   "Register for an event by choosing one of your identities": "S'inscrire à un évènement en choisissant une de vos identités",
   "Register on this instance": "S'inscrire sur cette instance",