Unify ContentMainDelegateEfl and WebProcessContentMainDelegateEfl

Unify ContentMainDelegateEfl and WebProcessContentMainDelegateEfl

Both classes are EWK delegates to the main process kick off routines.
It turns out though that chromium-efl is the only content-based
app that has two different delegates for browser and renderer processes.
Chrome (ChromeMainDelegate) and ContentShell (ShellMainDelegate) for
instance have this class unified.

That said, patch merges WebProcessContentMainDelegateEfl into
ContentMainDelegateEfl, simplifying our logic.
WebProcessContentMainDelegateEfl's main method PreSandboxStartup
was merged into ContentMainDelegateEfl counterpart.

Original beta/m47 patch:
- http://165.213.202.130/gerrit/#/c/105265/

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=14350

Reviewed by: djmix.kim, sns.park

Change-Id: Idff02ac417b8247d0fd498db7d99cf3a60b60fb7
Signed-off-by: Antonio Gomes <a1.gomes@samsung.com>