python3Packages.pytest-xdist: simplify setup hook

Same reasoning as commit before.

pkgs/development/python-modules/pytest-xdist/setup-hook.sh

@@ -4,21 +4,7 @@ pytestXdistHook() {
     )
 }
 
-# the flags should be added before pytestCheckHook runs so
-# until we have dependency mechanism in generic builder, we need to use this ugly hack.
-
 if [ -z "${dontUsePytestXdist-}" ] && [ -z "${dontUsePytestCheck-}" ]; then
-    if [[ " ${preDistPhases[*]:-} " =~ " pytestCheckPhase " ]]; then
-        _preDistPhases="${preDistPhases[*]} "
-        _preDistPhases="${_preDistPhases/ pytestCheckPhase / pytestXdistHook pytestCheckPhase }"
-        if [[ -n "${__structuredAttrs-}" ]]; then
-            preDistPhases=()
-        else
-            preDistPhases=""
-        fi
-        appendToVar preDistPhases $_preDistPhases
-        unset _preDistPhases
-    else
-        appendToVar preDistPhases pytestXdistHook
-    fi
+    # The flags should be added before pytestCheckHook runs in preDistPhases.
+    preInstallCheckHooks+=(pytestXdistHook)
 fi