Use unique_ptr for pwalletMain,httpRPCTimerInterface,dbw,dbenv,pdbCopy

Summary:
Partial backport of core PR11043

The following commits from this PR are backported:

• 860e912, 5a6f768, 0024531, 29ab96d, b45c597 in this diff
• 8ccf1bb, f72cbf9 in D1769
• d223bc9 in D1910

73db063 is no longer needed since D1765

Remaining:

• fa6d122 for fees in TxConfirmStats
• 8617989, 3e09b39, a357293 to introduce MakeUnique (later diff)

Test Plan:

make check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2229