registration: Fix `full_name` mapping in LDAP registration flow.
registration: Fix `full_name` mapping in LDAP registration flow.

We forgot to change this part of codebase when introduced changes
to allow split full name mapping in LDAP.

andersk/zulip,synicalsyntax/zulip,kou/zulip,zulip/zulip,hackerkid/zulip,eeshangarg/zulip,timabbott/zulip,andersk/zulip,rishig/zulip,rishig/zulip,timabbott/zulip,synicalsyntax/zulip,showell/zulip,tommyip/zulip,andersk/zulip,kou/zulip,eeshangarg/zulip,timabbott/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,punchagan/zulip,tommyip/zulip,synicalsyntax/zulip,eeshangarg/zulip,hackerkid/zulip,rishig/zulip,punchagan/zulip,shubhamdhama/zulip,showell/zulip,kou/zulip,punchagan/zulip,rht/zulip,punchagan/zulip,rishig/zulip,shubhamdhama/zulip,kou/zulip,showell/zulip,andersk/zulip,rishig/zulip,tommyip/zulip,zulip/zulip,kou/zulip,rht/zulip,shubhamdhama/zulip,showell/zulip,brainwane/zulip,eeshangarg/zulip,brainwane/zulip,brainwane/zulip,eeshangarg/zulip,tommyip/zulip,hackerkid/zulip,andersk/zulip,shubhamdhama/zulip,brainwane/zulip,brainwane/zulip,timabbott/zulip,synicalsyntax/zulip,rht/zulip,kou/zulip,timabbott/zulip,shubhamdhama/zulip,brainwane/zulip,timabbott/zulip,punchagan/zulip,tommyip/zulip,shubhamdhama/zulip,rht/zulip,rishig/zulip,synicalsyntax/zulip,synicalsyntax/zulip,kou/zulip,hackerkid/zulip,timabbott/zulip,tommyip/zulip,shubhamdhama/zulip,synicalsyntax/zulip,andersk/zulip,showell/zulip,rishig/zulip,brainwane/zulip,rht/zulip,rht/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,zulip/zulip,zulip/zulip,hackerkid/zulip,showell/zulip,showell/zulip,eeshangarg/zulip,tommyip/zulip