remove SmartPtr in favour of std::unique_ptr or std::shared_ptr

[MichaelRawson]

We have this SharedPtr thing, but it's essentially std::shared_ptr with extra hazard. Remove it.

Some of the occurrences were essentially std::unique_ptr, which is good news, we can save some cycles there. Still to do:

• check that ResultSubstitutionSP really needs to be shared they probably don't really, but it would be a huge change
• use std::make_shared where possible
• make sure nothing's gone wrong with perf

Also: remove some extraneous includes from header files and then fix up the resulting missing includes elsewhere. And the sanitiser was complaining correctly about a null dereference in the TPTP parser.