clean up legacy Python Venv on first launch

lib.include.sh

@@ -131,6 +131,14 @@ function activate_python_venv {
     export OT_PYTHON_CMD="python"
 }
 
+function remove_legacy_venv {
+    # Removes the legacy "venv" sub-directory from OneTrainer's directory.
+    if [[ -d "venv" ]]; then
+        print "Cleaning up legacy Python Venv environment in \"venv\"..."
+        rm -rfv "venv"
+    fi
+}
+
 # Conda command wrappers.
 function run_conda {
     print "+ ${OT_CONDA_CMD} $*"
@@ -298,6 +306,9 @@ function exit_if_active_env_wrong_python_version {
 
 # Performs the most important startup sanity checks and environment preparation.
 function prepare_runtime_environment {
+    # Clean up the legacy "venv" if it exists.
+    remove_legacy_venv
+
     # Ensure that the chosen Conda or Python runtime exists.
     exit_if_no_runtime