Drop zfp from makedepends

The vtkzfp module is marked as internal (vtk_module_third_party_internal())
so the build cannot use external zfp without patching.

https://docs.vtk.org/en/latest/api/cmake/ModuleSystem.html#third-party

.SRCINFO

@@ -58,7 +58,6 @@ pkgbase = vtk
 	makedepends = utf8cpp
 	makedepends = verdict
 	makedepends = xz
-	makedepends = zfp
 	makedepends = zlib
 	depends = double-conversion
 	depends = gcc-libs

PKGBUILD

@@ -76,7 +76,6 @@ makedepends=(
   utf8cpp
   verdict
   xz
-  zfp
   zlib
 )
 # pegtl: https://gitlab.kitware.com/vtk/vtk/-/issues/18151