css: Remove ignored CSS property in settings.scss.
css: Remove ignored CSS property in settings.scss.

`margin-bottom` property is ignored due to the display.With
'display: inline', the width, height, margin-top, margin-bottom,and
float properties have no effect.
brainwane/zulip,eeshangarg/zulip,punchagan/zulip,rht/zulip,showell/zulip,showell/zulip,andersk/zulip,zulip/zulip,timabbott/zulip,eeshangarg/zulip,timabbott/zulip,kou/zulip,punchagan/zulip,andersk/zulip,timabbott/zulip,brainwane/zulip,synicalsyntax/zulip,rht/zulip,timabbott/zulip,timabbott/zulip,synicalsyntax/zulip,shubhamdhama/zulip,synicalsyntax/zulip,brainwane/zulip,shubhamdhama/zulip,shubhamdhama/zulip,zulip/zulip,andersk/zulip,synicalsyntax/zulip,hackerkid/zulip,kou/zulip,kou/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,brainwane/zulip,kou/zulip,rht/zulip,punchagan/zulip,punchagan/zulip,hackerkid/zulip,shubhamdhama/zulip,zulip/zulip,eeshangarg/zulip,synicalsyntax/zulip,andersk/zulip,shubhamdhama/zulip,kou/zulip,showell/zulip,hackerkid/zulip,timabbott/zulip,timabbott/zulip,hackerkid/zulip,brainwane/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,showell/zulip,shubhamdhama/zulip,shubhamdhama/zulip,zulip/zulip,rht/zulip,showell/zulip,punchagan/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,brainwane/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,brainwane/zulip,synicalsyntax/zulip,showell/zulip,punchagan/zulip,punchagan/zulip,eeshangarg/zulip,showell/zulip