Remove unused htmx/json-enc vendor libs; fix missing htm.js symlink

- Remove vendor/htmx-2.0.4.min.js and vendor/json-enc-2.0.0.js (unused)
- Remove webui/static/htmx.min.js and webui/static/json-enc.js symlinks
- Add webui/static/vendor/htm.js symlink pointing to project root
  vendor/htm.js, fixing the module script MIME type error caused by
  hoover/html.js importing from a non-existent path

vendor/json-enc-2.0.0.js

@@ -1,12 +0,0 @@
-htmx.defineExtension('json-enc', {
-  onEvent: function(name, evt) {
-    if (name === 'htmx:configRequest') {
-      evt.detail.headers['Content-Type'] = 'application/json'
-    }
-  },
-
-  encodeParameters: function(xhr, parameters, elt) {
-    xhr.overrideMimeType('text/json')
-    return (JSON.stringify(parameters))
-  }
-})