Don't set interpolation_method_ twice

[AndyZe]

Previously it was set in on_init() L61 and also in on_configure() L698.

[codecov-commenter]

Codecov Report

Merging #517 (2be6292) into master (e7f9962) will decrease coverage by 3.31%.
The diff coverage is 26.60%.

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@@            Coverage Diff             @@
##           master     #517      +/-   ##
==========================================
- Coverage   35.78%   32.48%   -3.31%     
==========================================
  Files         189        7     -182     
  Lines       17570      665   -16905     
  Branches    11592      357   -11235     
==========================================
- Hits         6287      216    -6071     
+ Misses        994      157     -837     
+ Partials    10289      292    -9997     

Flag	Coverage Δ
unittests	32.48% <26.60%> (-3.31%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ontroller/test/test_load_diff_drive_controller.cpp	12.50% <0.00%> (ø)
diff_drive_controller/src/odometry.cpp	42.16% <11.11%> (ø)
diff_drive_controller/src/speed_limiter.cpp	46.55% <11.11%> (ø)
...ive_controller/test/test_diff_drive_controller.cpp	17.62% <12.08%> (ø)
...troller/include/diff_drive_controller/odometry.hpp	20.00% <20.00%> (ø)
...iff_drive_controller/src/diff_drive_controller.cpp	39.22% <35.50%> (ø)
...de/diff_drive_controller/diff_drive_controller.hpp	100.00% <100.00%> (ø)
..._controllers/src/joint_group_effort_controller.cpp
...ller/test/test_load_forward_command_controller.cpp
...dcaster/test/test_load_joint_state_broadcaster.cpp
... and 191 more

[bmagyar]

thank you, here's a 🥠 for your trouble!! :D