drop GRAAL_PYTHON_ARGS from env after it was parsed

(cherry picked from commit a8aded0)

Author: tomasstupka

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/PosixModuleBuiltins.java

@@ -314,6 +314,11 @@ public void postInitialize(Python3Core core) {
         PDict environ = core.factory().createDict();
         String pyenvLauncherKey = "__PYVENV_LAUNCHER__";
         for (Entry<String, String> entry : getenv.entrySet()) {
+            if(entry.getKey().equals("GRAAL_PYTHON_ARGS")) {
+                // was already processed at startup in GraalPythonMain and
+                // we don't want subprocesses to pick it up
+                continue;
+            }
             Object key, val;
             if (PythonOS.getPythonOS() == PythonOS.PLATFORM_WIN32) {
                 key = toTruffleStringUncached(entry.getKey());