portico: Remove style selector for superflous button.grey-transparent.
portico: Remove style selector for superflous button.grey-transparent.

There is no element with the .grey-transparent class in the current
codebase, so it is likely legacy and thus unnecessary.

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