Deprecate browserify support

[Johennes]

We currently provide dedicated builds of matrix-js-sdk for direct use in browsers with every release. These are backed by browserify and in order to limit the bundle size, they don't include libolm. Instead the latter has to be loaded via a separate <script> tag. The mechanics of this split are not trivial though and are an impediment for integrating Element R.

At the same time, usage of the browser-targeted assets seems fairly low right now – at least when looking at direct download of the GitHub artifacts. The below numbers are from v23.0.0.

Since we also release on npm, this doesn't tell the full story of course.

If you are currently a user of the browser version of matrix-js-sdk, we'd like to hear about your use case to better inform our decision about whether or not to deprecate this release channel.

[Johennes]

Duplicate of matrix-org/matrix-js-sdk#3189