PYMUPDF_SETUP_REQUIRE_LAYOUT_4LLM=0 drops the empty pymupdf_layout and
pymupdf4llm transition packages from Requires-Dist, but the hyphenated
pymupdf-layout spelling is added unconditionally. Gate it the same way.

--- a/setup.py
+++ b/setup.py
@@ -263,11 +263,11 @@
             'numpy',
             'onnxruntime',
             'pyyaml',
-            f'pymupdf-layout=={version_p}',
             ]
 
     if PYMUPDF_SETUP_REQUIRE_LAYOUT_4LLM != '0':
         g_requires_dist += [
+                f'pymupdf-layout=={version_p}',
                 f'pymupdf_layout=={version_p}',
                 ]