Before ghc-7.2 hs_add_root() had to be used to initialize haskell
modules when haskell was called from FFI.

commit a52ff761


("Change the way module initialisation is done (#3252, #4417)")
removed needs for hs_add_root() and made function a no-op.
For backward compatibility '__stginit_<module>' symbol was
not removed.

This change removes no-op hs_add_root() function and unused
'__stginit_<module>' symbol from each haskell module.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: ./validate

Reviewers: simonmar, austin, bgamari, erikd

Reviewed By: simonmar

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3460