CLN: avoid _internal_get_values in groupby.generic (#32427)

Author: simonjayhawkins

pandas/core/groupby/generic.py

@@ -589,7 +589,7 @@ def nunique(self, dropna: bool = True) -> Series:
         """
         ids, _, _ = self.grouper.group_info
 
-        val = self.obj._internal_get_values()
+        val = self.obj._values
 
         codes, _ = algorithms.factorize(val, sort=False)
         sorter = np.lexsort((codes, ids))
@@ -657,7 +657,7 @@ def value_counts(
             )
 
         ids, _, _ = self.grouper.group_info
-        val = self.obj._internal_get_values()
+        val = self.obj._values
 
         # groupby removes null keys from groupings
         mask = ids != -1
@@ -774,7 +774,7 @@ def count(self) -> Series:
             Count of values within each group.
         """
         ids, _, ngroups = self.grouper.group_info
-        val = self.obj._internal_get_values()
+        val = self.obj._values
 
         mask = (ids != -1) & ~isna(val)
         ids = ensure_platform_int(ids)