Remove compensation flag for kinetic pressure contribution

[fweik]

Description of changes:

• Fixed kinetic pressure compensation in pressure observable
• Do not depend on NpT instantanuous pressure in pressure observable calc
• Removed no unneeded v_comp flag for compensated kinetic pressure

[jngrad]

LGTM

[codecov]

Codecov Report

Merging #3756 into python will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           python   #3756   +/-   ##
======================================
  Coverage      89%     89%           
======================================
  Files         552     552           
  Lines       24559   24532   -27     
======================================
- Hits        21886   21875   -11     
+ Misses       2673    2657   -16     

Impacted Files	Coverage Δ
src/core/communication.hpp	100% <ø> (ø)
src/core/event.cpp	93% <ø> (-1%)	⬇️
src/core/npt.cpp	88% <ø> (-1%)	⬇️
src/core/Observable_stat.hpp	100% <100%> (ø)
src/core/communication.cpp	94% <100%> (-1%)	⬇️
src/core/pressure.cpp	100% <100%> (+17%)	⬆️
src/core/pressure_inline.hpp	85% <100%> (-1%)	⬇️
src/core/particle_data.cpp	96% <0%> (-1%)	⬇️
src/core/polymer.cpp	98% <0%> (+6%)	⬆️

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