Remove tw_hit_test

Remove tw_hit_test

There were two distinct classes: Ewk_Hit_Test and _Ewk_Hit_Test.
Ewk_Hit_Test was a subclass of tizen_webview::Hit_Test _Ewk_Hit_Test
owned an Ewk_Hit_Test and accessed it's properties.

This patch simplifies everything: there is now only _Ewk_Hit_Test, and
Ewk_Hit_Test is an alias to it.

Bug: http://web.sec.samsung.net/bugzilla/show_bug.cgi?id=11619

Change-Id: I885c5c8350f306b44c2d8ed19ab1c9a2ff43894a
Signed-off-by: Arnaud Renevier <a.renevier@samsung.com>