Revert "url: support `path` for url.format"

This reverts commit d312b6d1.

d312b6d1 introduced some confusion in
the existing API of url.format and url.parse.

The way the 'path' property overrides other properties in url.format's
input is too confusing for existing users compared to the issues it
fixes.

Fixes such as https://github.com/joyent/node/pull/9081 have been
proposed, but they do not make the API less confusing.

Instead, this change just reverts the original breaking change so that
it gives us more time after v0.12.0 is released to come up with a better
API for url.format, url.parse and other related APIs in the v0.13
development branch.

Fixes #9070.

Conflicts:
	doc/api/url.markdown

PR: #9109
PR-URL: https://github.com/joyent/node/pull/9109


Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>