weechatScripts.weechat-matrix-bridge: don't export `olm.lua' as script (#46582)

Loading olm.lua as weechat script with `/script load olm.lua' causes
errors like this:

```
/nix/store/43jbh7yxh8j4gjfzbvpd9clncah5dip1-weechat-matrix-bridge-2018-05-29/lib/ffi.so: undefined symbol: lua_tointeger
```

As `olm.lua' is loaded by `matrix.lua' it doesn't need to be included
manually by the weechat configuration.