topic list: Rename remove_expanded_topics() to clear().
topic list: Rename remove_expanded_topics() to clear().

The name clear() is more concise and captures the notion
that we're not just clearing the DOM, we're clearing our
internal data structures.

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