Minor fixes based on lgtm.com alerts (#6819)

* Remove a couple of superfluous trailing arguments

* Simplify assignment logic in a couple of places

* Modify some potentially inconsistent setState calls to use the function form

* Fix eslint errors

webapp/components/post_view/post_attachment.jsx

@@ -55,10 +55,11 @@ export default class PostAttachment extends React.PureComponent {
 
     toggleCollapseState(e) {
         e.preventDefault();
-
-        this.setState({
-            text: this.state.collapsed ? this.state.uncollapsedText : this.state.collapsedText,
-            collapsed: !this.state.collapsed
+        this.setState((prevState) => {
+            return {
+                text: prevState.collapsed ? prevState.uncollapsedText : prevState.collapsedText,
+                collapsed: !prevState.collapsed
+            };
         });
     }
 

webapp/components/post_view/post_body_additional_content.jsx

@@ -62,7 +62,9 @@ export default class PostBodyAdditionalContent extends React.PureComponent {
     }
 
     toggleEmbedVisibility() {
-        this.setState({embedVisible: !this.state.embedVisible});
+        this.setState((prevState) => {
+            return {embedVisible: !prevState.embedVisible};
+        });
     }
 
     getSlackAttachment() {