Use std::unique_ptr (C++11) where possible

Summary:

• Use unique_ptr for pfilter (CBloomFilter)
• Use unique_ptr for sem{Addnode,Outbound} (CSemaphore)

This is part of Core PR11043

Test Plan:

make check

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1769