revert: fix($location): return '/' for root path in hashbang mode

This reverts commit 63cd873.

The change breaks existing tests of Google apps. The problem is that
while we tried to avoid adding #/ to window.location.href unnecessarily
we failed doing so. Likely because by setting $path, at some point
(during a digest) we try to check if $location changed and we mistake the
default '/' with an explicit settign of the path via the `path()` method.
This results in us writing the url with '#/' into $browser.url() which updates
the window.location by adding "#/" to the url - something we tried to avoid
in the first place.

I'll reopen PR angular#5712.

src/ng/location.js

@@ -184,10 +184,6 @@ function LocationHashbangUrl(appBase, hashPrefix) {
 
     this.$$compose();
 
-    if (!this.$$path) {
-      this.$$path = '/';
-    }
-
     /*
      * In Windows, on an anchor node on documents loaded from
      * the filesystem, the browser will return a pathname

test/ng/locationSpec.js

@@ -1487,16 +1487,6 @@ describe('$location', function() {
       expect(location.url()).toBe('/not-starting-with-slash');
       expect(location.absUrl()).toBe('http://server/pre/index.html#/not-starting-with-slash');
     });
-
-
-    it("should return / for path for the application root path", function() {
-      location = new LocationHashbangUrl('http://server/pre/index.html', '#');
-      location.$$parse('http://server/pre/index.html');
-      expect(location.path()).toBe('/');
-
-      location.$$parse('http://server/pre/');
-      expect(location.path()).toBe('/');
-    });
   });