Remove unused percentiles_for_norm field and deprecation alias

The `percentiles_for_norm` field on `ImageRenderParams` and its
`quantiles_for_norm` deprecation alias were never wired into the
rendering pipeline. Per-channel normalization is now handled via
the `norm` parameter accepting a list of Normalize objects.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: timtreis

src/spatialdata_plot/pl/basic.py

@@ -505,7 +505,7 @@ def render_points(
 
         return sdata
 
-    @_deprecation_alias(elements="element", quantiles_for_norm="percentiles_for_norm", version="version 0.3.0")
+    @_deprecation_alias(elements="element", version="version 0.3.0")
     def render_images(
         self,
         element: str | None = None,

src/spatialdata_plot/pl/render_params.py

@@ -266,7 +266,6 @@ class ImageRenderParams:
     palette: ListedColormap | list[str] | None = None
     norms: list[Normalize] | None = None
     alpha: float = 1.0
-    percentiles_for_norm: tuple[float | None, float | None] = (None, None)
     scale: str | None = None
     zorder: int = 0
     colorbar: bool | str | None = "auto"