css: Remove redundant `.reaction_button` rule from reactions.scss.
css: Remove redundant `.reaction_button` rule from reactions.scss.

The removed rule does not apply in any case since it's always overridden
by `.message_reaction + .reaction_button` rule defined later on.

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