Fix unused var and pseudorandom warnings

src/lib/legacy/domParserTextHtml.js

@@ -22,7 +22,7 @@
             // text/html parsing is natively supported
             return;
         }
-    } catch (ex) { /* noop */ }
+    } catch { /* noop */ }
 
     DOMParserPrototype.parseFromString = function (markup, type) {
         if (/^\s*text\/html\s*(?:;|$)/i.test(type)) {

src/lib/legacy/keyboardEvent.js

@@ -8,7 +8,7 @@
 
     try {
         new window.KeyboardEvent('event', { bubbles: true, cancelable: true });
-    } catch (e) {
+    } catch {
         // We can't use `KeyboardEvent` in old WebKit because `initKeyboardEvent`
         // doesn't seem to populate some properties (`keyCode`, `which`) that
         // are read-only.

src/lib/legacy/patchHeaders.js

@@ -13,7 +13,7 @@
     if (window.Headers) {
         try {
             new window.Headers(undefined);
-        } catch (_) {
+        } catch {
             console.debug('patch \'Headers\' to accept \'undefined\'');
 
             const _Headers = window.Headers;