Only Interactive.js used it.

Otherwise, special characters (e.g. `+`) in the idaSystemURL will be
interpreted as encoded data and converted to spaces. Which means that, say,
`git+https` will end up as `git https`. And then Bad Stuff (tm) happens.

Per https://reactjs.org/docs/introducing-jsx.html#specifying-attributes-with-jsx.
Fixes broken links on the IDA page.