fix(headers): fixed & optimized clear method; (#5507)

lib/core/AxiosHeaders.js

@@ -174,8 +174,20 @@ class AxiosHeaders {
     return deleted;
   }
 
-  clear() {
-    return Object.keys(this).forEach(this.delete.bind(this));
+  clear(matcher) {
+    const keys = Object.keys(this);
+    let i = keys.length;
+    let deleted = false;
+
+    while (i--) {
+      const key = keys[i];
+      if(!matcher || matchHeaderValue(this, this[key], key, matcher)) {
+        delete this[key];
+        deleted = true;
+      }
+    }
+
+    return deleted;
   }
 
   normalize(format) {