bug#48927: VTK fails to build. (regression)

[lg188]

In a previous bugreport [1] a solution was added. VTK got updated to 9 [2].
To satisfy an issue with FreeCAD an VTK-8 was re-added [3]. But this
is an older version, that re-introduces a regression that was fixed in
[4]

[1] https://issues.guix.gnu.org/46246
[2] 
https://git.savannah.gnu.org/cgit/guix.git/commit/gnu/packages/image-processing.scm?id=48f7aa1cd104096daccc8a4859021f1e1177f525
[3] 
https://git.savannah.gnu.org/cgit/guix.git/commit/gnu/packages/image-processing.scm?id=950475bb963468c92fd7d47300010a584c7daf55
[4] 
https://git.savannah.gnu.org/cgit/guix.git/commit/?id=251b0f7a6fa550ef4e0975668d7ab8c4c7b214d3