Revert "3D lloyd et rtree"

This reverts commit ed1df8e16addb6b42cd1ccb620732a7d1c0426ed.

contrib/voro++/CMakeLists.txt

-set(SRC
-  src/voro++.cc
-)
-
-file(GLOB_RECURSE HDR RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} *.h)
-append_gmsh_src(contrib/voro++ "${SRC};${HDR}")

contrib/voro++/config.mk

-# Voro++, a 3D cell-based Voronoi library
-#
-# Author : Chris H. Rycroft (LBL / UC Berkeley)
-# Email  : chr@alum.mit.edu
-# Date   : August 28th 2011
-
-# This a common configuration file that includes definitions used by all
-# the Makefiles.
-
-# C++ compiler
-CXX=g++
-
-# Flags for the C++ compiler
-CFLAGS=-Wall -ansi -pedantic -O3
-
-# Relative include and library paths for compilation of the examples
-E_INC=-I../../src
-E_LIB=-L../../src
-
-# Installation directory
-PREFIX=/usr/local
-
-# Install command
-INSTALL=install
-
-# Flags for install command for executable
-IFLAGS_EXEC=-m 0755
-
-# Flags for install command for non-executable files
-IFLAGS=-m 0644