fpdf2: Remove redundant str | Literal['DEPRECATED'] union (#8650)

stubs/fpdf2/fpdf/fpdf.pyi

@@ -139,7 +139,7 @@ class FPDF:
         orientation: _Orientation = ...,
         unit: _Unit | float = ...,
         format: _Format | tuple[float, float] = ...,
-        font_cache_dir: str | Literal["DEPRECATED"] = ...,
+        font_cache_dir: Literal["DEPRECATED"] = ...,
     ) -> None: ...
     @property
     def font_size_pt(self) -> float: ...