CLN: remove unneeded checks

Author: toobaz

pandas/core/frame.py

@@ -4096,9 +4096,8 @@ def _maybe_casted_values(index, labels=None):
             if not isinstance(level, (tuple, list)):
                 level = [level]
             level = [self.index._get_level_number(lev) for lev in level]
-            if isinstance(self.index, MultiIndex):
-                if len(level) < self.index.nlevels:
-                    new_index = self.index.droplevel(level)
+            if len(level) < self.index.nlevels:
+                new_index = self.index.droplevel(level)
 
         if not drop:
             if isinstance(self.index, MultiIndex):

pandas/core/series.py

@@ -1199,9 +1199,8 @@ def reset_index(self, level=None, drop=False, name=None, inplace=False):
                 if not isinstance(level, (tuple, list)):
                     level = [level]
                 level = [self.index._get_level_number(lev) for lev in level]
-                if isinstance(self.index, MultiIndex):
-                    if len(level) < self.index.nlevels:
-                        new_index = self.index.droplevel(level)
+                if len(level) < self.index.nlevels:
+                    new_index = self.index.droplevel(level)
 
             if inplace:
                 self.index = new_index