push_notifications: Handle errors with token reuse.
push_notifications: Handle errors with token reuse.

If an Android token has been used to connect a given device with
multiple Zulip servers, and then is expired, we would 500 in trying to
remove the Zulip-side registration for it, because the code assumed
there was only one such registration.  If a token is no longer valid,
it's invalid for all servers, so the correct fix is to just remove them all.

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