ldap docs: LDAP backend now works for initial realm creation.
ldap docs: LDAP backend now works for initial realm creation.

Fixes #9576.

Initial realm creation now works fine with the LDAP backend, so the
part of the docs about needing to create the first realm with the
email backend is unnecessary and just complicates the setup process,
so it seems best to just remove it.

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