Protect destructors of some template classes

[KaustubhShamshery]

Description

Zilliqa/Issues/issues/507

Ref Item No. 4 http://www.gotw.ca/publications/mill18.htm

a) you want to allow polymorphic deletion through a base pointer, in which case the destructor must be virtual and public; or b) you don't, in which case the destructor should be nonvirtual and protected, the latter to prevent the unwanted usage.

Backward Compatibility

• This is not a breaking change
• This is a breaking change

Review Suggestion

Status

Implementation

• ready for review

Integration Test (Core Team)

• local machine test

• small-scale cloud test

[codecov-io]

Codecov Report

Merging #1655 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1655   +/-   ##
=======================================
  Coverage   33.53%   33.53%           
=======================================
  Files         269      269           
  Lines       32757    32757           
=======================================
  Hits        10984    10984           
  Misses      21773    21773

Impacted Files	Coverage Δ
src/libServer/Server.h	0% <ø> (ø)	⬆️
src/libData/BlockChainData/BlockChain.h	92.3% <100%> (ø)	⬆️

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