Revert "url: delete href cache on all setter code paths"

This reverts commit dbdd81a.

It was agreed that this change contained too much potential ecosystem
breakage, particularly around the inability to `delete` properties off a
`Url` object. It may be re-introduced for a later release, along with
better work on ecosystem compatibility.

PR-URL: #1602
Reviewed-By: Mikeal Rogers <mikeal.rogers@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Forrest L Norvell <forrest@npmjs.com>
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Isaac Z. Schlueter <i@izs.me>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/url.js

@@ -1041,8 +1041,8 @@ Object.defineProperty(Url.prototype, 'host', {
         this._port = -1;
         this._hostname = this._host = encodeURIComponent(host);
       }
+      this._href = '';
     }
-    this._href = '';
   },
   enumerable: true,
   configurable: true
@@ -1068,8 +1068,9 @@ Object.defineProperty(Url.prototype, 'hostname', {
         this._host = hostname + ':' + this._port;
       else
         this._host = hostname;
+
+      this._href = '';
     }
-    this._href = '';
   },
   enumerable: true,
   configurable: true
@@ -1088,8 +1089,8 @@ Object.defineProperty(Url.prototype, 'hash', {
         hash = '#' + hash;
       }
       this._hash = hash;
+      this._href = '';
     }
-    this._href = '';
   },
   enumerable: true,
   configurable: true
@@ -1113,8 +1114,8 @@ Object.defineProperty(Url.prototype, 'search', {
       if (this._parsesQueryStrings) {
         this.query = querystring.parse(search.slice(1));
       }
+      this._href = '';
     }
-    this._href = '';
   },
   enumerable: true,
   configurable: true
@@ -1137,8 +1138,8 @@ Object.defineProperty(Url.prototype, 'pathname', {
       }
 
       this._pathname = pathname;
+      this._href = '';
     }
-    this._href = '';
   },
   enumerable: true,
   configurable: true