Update on "[Executorch][CI] Fix qnn runner ci job scripts"

QNN backend's AOT artifacts were being copied in the source directory instead of
them being installed, as build artifacts, in appropriate package directory.

As a result we had to use PYTHON_PATH=".." in test_llama.sh CI script when
running CI for qnn. This results in executorch having two locations as where
the package is installed. This PR fixes that.

Differential Revision: [D66406274](https://our.internmc.facebook.com/intern/diff/D66406274/)

[ghstack-poisoned]

Author: kimishpatel

.ci/scripts/test_model.sh

@@ -152,10 +152,8 @@ test_model_with_qnn() {
   source "$(dirname "${BASH_SOURCE[0]}")/build-qnn-sdk.sh"
   echo "ANDROID_NDK_ROOT: $ANDROID_NDK_ROOT"
   echo "QNN_SDK_ROOT: $QNN_SDK_ROOT"
-  echo "EXECUTORCH_ROOT: $EXECUTORCH_ROOT"
 
   export LD_LIBRARY_PATH=$QNN_SDK_ROOT/lib/x86_64-linux-clang/
-  export PYTHONPATH=$EXECUTORCH_ROOT/..
 
   if [[ "${MODEL_NAME}" == "dl3" ]]; then
     EXPORT_SCRIPT=deeplab_v3