refactor: Omit unused exception arguments from catch blocks (#8559)

Fixes #1770.

appengine/blockly_compressed.js

@@ -6,6 +6,6 @@ var msg = 'Compiled Blockly files should be loaded from https://unpkg.com/blockl
 console.log(msg);
 try {
   alert(msg);
-} catch (_e) {
+} catch {
   // Can't alert?  Probably node.js.
 }

scripts/gulpfiles/build_tasks.js

@@ -699,7 +699,7 @@ function buildAdvancedCompilationTest() {
   // a later browser-based test won't check it should the compile fail.
   try {
     fs.unlinkSync('./tests/compile/main_compressed.js');
-  } catch (_e) {
+  } catch {
     // Probably it didn't exist.
   }
 

tests/compile/main.js

@@ -47,7 +47,7 @@ window['healthCheck'] = function() {
     const blockCount =
         getMainWorkspace().getFlyout().getWorkspace().getTopBlocks().length;
     return (blockCount > 5 && blockCount < 100);
-  } catch (_e) {
+  } catch {
     return false;
   }
 };