Remove unnecessary private method from ACTS pixel Clustering tool

A remnant from previous versions of the code. Can be removed

added ACTS bugfix labels

This merge request affects 1 package:

• Tracking/Acts/ActsDataPreparation

This merge request affects 2 files:

• Tracking/Acts/ActsDataPreparation/src/PixelClusteringTool.cxx
• Tracking/Acts/ActsDataPreparation/src/PixelClusteringTool.h

Adding @lshan ,@tbold ,@battagl ,@jojungge ,@stsuno ,@cvarni ,@pagessin ,@toyamaza as watchers

added Tracking main review-pending-level-1 labels

CI Result SUCCESS (hash 8915720c)

	Athena
externals
cmake
make
tests

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Athena: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-EL9 10108] (remote access info)

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 6d4cc5a7