drop Python 2.6 support

INSTALL.md

@@ -40,7 +40,7 @@ Sub-points here discuss prerequisites needed to build CP2K. Copies of the recomm
 GNU make should be on your system (gmake or make on linux) and used for the build, go to https://www.gnu.org/software/make/make.html download from https://ftp.gnu.org/pub/gnu/make/ also Python (2.x) is required for building.
 
 ### 2b. Python (required, build system)
-Python 2.x is needed to run the dependency generator. On most system Python is already installed. For more information visit: https://www.python.org/
+Python 2.7 or 3.5+ is needed to run the dependency generator. On most system Python is already installed. For more information visit: https://www.python.org/
 
 ### 2c. Fortran and C Compiler (required, build system)
 A Fortran 2008 compiler and matching C compiler should be installed on your system. We have good experience with gcc/gfortran (gcc >=4.6 works, later version recommended). Be aware that some compilers have bugs that might cause them to fail (internal compiler errors, segfaults) or, worse, yield a mis-compiled CP2K. Report bugs to compiler vendors; they (and we) have an interest in fixing them. A list of tested compiler can be found [here](https://www.cp2k.org/dev:compiler_support). Always run a `make -j test` (See point 5.) after compilation to identify these problems.

tools/docker/scripts/install_python.sh

@@ -23,18 +23,3 @@ rm -rf /var/lib/apt/lists/*
 # install python packages
 pip  install --quiet numpy matplotlib requests
 pip3 install --quiet numpy matplotlib requests pre-commit
-
-# install python2.6
-echo "Building Python-2.6.9... "
-cd /tmp
-wget -q https://www.python.org/ftp/python/2.6.9/Python-2.6.9.tgz
-echo "7277b1285d8a82f374ef6ebaac85b003266f7939b3f2a24a3af52f9523ac94db  Python-2.6.9.tgz" | sha256sum --check
-tar -xzf Python-2.6.9.tgz
-pushd Python-2.6.9
-./configure > /tmp/python2.6.9_configure.log
-make -j  > /tmp/python2.6.9_make.log
-make install > /tmp/python2.6.9_install.log
-popd
-rm -rf Python-2.6.9*
-
-#EOF

tools/docker/scripts/test_python.sh

@@ -46,9 +46,6 @@ cd /workspace/cp2k
 ALL_TEST_SCRIPTS=$(find ./src/ ./tools/ -name "*_test.py"  -executable)
 ESSENTIAL_TEST_SCRIPTS=$(find ./tools/build_utils -name "*_test.py"  -executable)
 
-# python 2.6
-run_tests python2.6 "${ESSENTIAL_TEST_SCRIPTS}"
-
 # python 2.7
 run_tests python2.7 "${ALL_TEST_SCRIPTS}"