add 'kernel_only=True' to RemoveCallsTransformation

[MichaelSt98]

add kernel_only=True to RemoveCallsTransformation to avoid DrHook Calls being removed from driver routines.

This was part of the loki_transform.py ecphys() entry point, but not yet part of the convert() entry point. Tested with/for ecphys.

[github-actions]

Documentation for this branch can be viewed at https://sites.ecmwf.int/docs/loki/185/index.html

[codecov]

Codecov Report

Merging #185 (6f695b4) into main (af8ec9f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #185   +/-   ##
=======================================
  Coverage   92.14%   92.14%           
=======================================
  Files          90       90           
  Lines       16690    16690           
=======================================
  Hits        15379    15379           
  Misses       1311     1311           

Flag	Coverage Δ
lint_rules	96.22% <ø> (ø)
loki	92.11% <ø> (ø)
transformations	91.40% <ø> (ø)

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[reuterbal]

Uncontroversial, I think. Looks good to me, many thanks!