i18n: Fix type signature of withGetText.
i18n: Fix type signature of withGetText.

The return type was backward: it tried to add `_: GetText` to the
component's props type, rather than subtract it.

The error had gone unnoticed because the one initial consumer of
this API, namely MessageList, has type-checking defeated by the
untyped `connectActionSheet`.

Thanks to @anh2111 (in #3231) for reporting this issue.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile