Fix deprecation issues with older Python code (#296)

* Fix deprecation issues with older Python code

* Remove mbed_greentea package

Author: Jamie Smith

.github/workflows/basic_checks.yml

@@ -158,7 +158,6 @@ jobs:
           doxyfile-path: ./doxyfile_options
 
   python-tests:
-    # these tests run in 3.7, hence running in vm not in pre-built docker
     runs-on: ubuntu-latest
     steps:
       -

tools/cmake/mbed-run-greentea-test.in.cmake

@@ -16,7 +16,6 @@ set(MBEDHTRUN_ARGS --skip-flashing @MBED_HTRUN_ARGUMENTS@) # filled in by config
 string(REPLACE ";" " " MBEDHTRUN_ARGS_FOR_DISPLAY "${MBEDHTRUN_ARGS}")
 message("Executing: @Python3_EXECUTABLE@ -m mbed_host_tests.mbedhtrun ${MBEDHTRUN_ARGS_FOR_DISPLAY}")
 
-# Note: For this command, we need to survive mbedhtrun not being on the PATH, so we import the package and call the main function using "python -c"
 execute_process(
 	COMMAND @Python3_EXECUTABLE@ -m mbed_host_tests.mbedhtrun ${MBEDHTRUN_ARGS}
 	WORKING_DIRECTORY "@mbed-os_SOURCE_DIR@/tools/python"