V14 compatible depenendencies (#66)

* Downgrade dependencies to match V14 versions.

https://github.com/vaadin/platform/blob/14.6/versions.json used as source for version numbers.

* Remove version func from styling-components

input-button, input-text, and message-avatar exist so that you can theme them more easily.
Coverage test was failing because the version function was never executed.
Looking at other components, these theming-purposed components do not have version function, and are not tested.
I removed the version functions for these component to follow the pattern of other components.

* message-avatar also.

package.json

@@ -58,12 +58,12 @@
   },
   "dependencies": {
     "@polymer/polymer": "^3.0.0",
-    "@vaadin/vaadin-avatar": "^2.0.0",
+    "@vaadin/vaadin-avatar": "^1.0.4",
     "@vaadin/vaadin-button": "^2.4.0",
     "@vaadin/vaadin-element-mixin": "^2.4.2",
     "@vaadin/vaadin-lumo-styles": "^1.6.1",
     "@vaadin/vaadin-material-styles": "^1.3.2",
-    "@vaadin/vaadin-text-field": "^3.0.1",
+    "@vaadin/vaadin-text-field": "^2.8.4",
     "@vaadin/vaadin-themable-mixin": "^1.6.2"
   },
   "devDependencies": {

src/vaadin-message-avatar.js

@@ -33,10 +33,6 @@ class MessageAvatarElement extends AvatarElement {
   static get is() {
     return 'vaadin-message-avatar';
   }
-
-  static get version() {
-    return '2.0.0-alpha2';
-  }
 }
 
 customElements.define(MessageAvatarElement.is, MessageAvatarElement);

src/vaadin-message-input-button.js

@@ -33,10 +33,6 @@ class MessageInputButtonElement extends ButtonElement {
   static get is() {
     return 'vaadin-message-input-button';
   }
-
-  static get version() {
-    return '2.0.0-alpha2';
-  }
 }
 
 customElements.define(MessageInputButtonElement.is, MessageInputButtonElement);

src/vaadin-message-input-text-area.js

@@ -35,10 +35,6 @@ class MessageInputTextAreaElement extends TextAreaElement {
     return 'vaadin-message-input-text-area';
   }
 
-  static get version() {
-    return '2.0.0-alpha2';
-  }
-
   static get properties() {
     return {
       ariaLabel: {