cache: Remove a now-unnecessary TODO.
cache: Remove a now-unnecessary TODO.

We solved the problem the TODO raised by using a different type
annotation syntax, and I'm not sure whether that refactor would
actually improve the code.

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