Revert "Fix missing comments in diff-view"

This reverts commit c71814fa0c.

Reason for revert: multiple reports like https://imgur.com/ClTwpKw

Change-Id: Id2e22f7cfe875b294e140c35177368a5cdbd5756

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js

@@ -815,9 +815,10 @@
         // for each line from the start.
         let lastEl;
         for (const threadEl of addedThreadEls) {
+          const lineNumString = threadEl.getAttribute('line-num') || 'FILE';
           const commentSide = threadEl.getAttribute('comment-side');
-          const lineEl = this._getLineElement(threadEl,
-              commentSide);
+          const lineEl = this.$.diffBuilder.getLineElByNumber(
+              lineNumString, commentSide);
           const contentText = this.$.diffBuilder.getContentByLineEl(lineEl);
           const contentEl = contentText.parentElement;
           const threadGroupEl = this._getOrCreateThreadGroup(
@@ -843,18 +844,6 @@
       });
     }
 
-    _getLineElement(threadEl, commentSide) {
-      const lineNumString = threadEl.getAttribute('line-num') || 'FILE';
-      const lineEl = this.$.diffBuilder.getLineElByNumber(
-          lineNumString, commentSide);
-      if (lineEl) {
-        return lineEl;
-      }
-      // It is possible to add comment to non-existing line via API
-      threadEl.invalidLineNumber = true;
-      return this.$.diffBuilder.getLineElByNumber('FILE', commentSide);
-    }
-
     _unobserveIncrementalNodes() {
       if (this._incrementalNodeObserver) {
         Polymer.dom(this).unobserveNodes(this._incrementalNodeObserver);

polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.html

@@ -16,8 +16,6 @@ limitations under the License.
 -->
 
 <link rel="import" href="/bower_components/polymer/polymer.html">
-<link rel="import" href="/bower_components/iron-icon/iron-icon.html">
-<link rel="import" href="../../shared/gr-icons/gr-icons.html">
 <link rel="import" href="../../../behaviors/fire-behavior/fire-behavior.html">
 <link rel="import" href="../../../behaviors/gr-path-list-behavior/gr-path-list-behavior.html">
 <link rel="import" href="../../../styles/shared-styles.html">
@@ -80,18 +78,6 @@ limitations under the License.
         margin-left: var(--spacing-m);
         font-style: italic;
       }
-      .invalidLineNumber {
-        padding: var(--spacing-m);
-      }
-      .invalidLineNumberText {
-        color: var(--error-text-color);
-      }
-      .invalidLineNumberIcon {
-        color: var(--error-text-color);
-        vertical-align: top;
-        margin-right: var(--spacing-s);
-      }
-
     </style>
     <template is="dom-if" if="[[showFilePath]]">
       <div class="pathInfo">
@@ -100,11 +86,6 @@ limitations under the License.
       </div>
     </template>
     <div id="container" class$="[[_computeHostClass(unresolved, isRobotComment)]]">
-      <template is="dom-if" if="[[invalidLineNumber]]">
-        <div class="invalidLineNumber">
-          <span class="invalidLineNumberText"><iron-icon icon="gr-icons:error" class="invalidLineNumberIcon"></iron-icon>This comment thread is attached to non-existing line [[lineNum]].</span>
-        </div>
-      </template>
       <template id="commentList" is="dom-repeat" items="[[_orderedComments]]"
           as="comment">
         <gr-comment

polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.js

@@ -124,11 +124,6 @@
           type: Boolean,
           value: false,
         },
-        /** It is possible to add comment to non-existing line via API */
-        invalidLineNumber: {
-          type: Number,
-          reflectToAttribute: true,
-        },
         /** Necessary only if showFilePath is true or when used with gr-diff */
         lineNum: {
           type: Number,