[Python] Pybind11 version, setup.py documentation

Pybind11 2.10 has a bug related to binding enums. Somehow exposed by a
totally unrelated commit 62cb3d109e.
Upgrading past 2.10 fixed it.

Also fixing some setup.py comments.

lib/Bindings/Python/pyproject.toml

@@ -6,7 +6,8 @@ requires = [
     "cmake>=3.12",
     # MLIR build depends.
     "numpy",
-    "pybind11>=2.9",
+    # Pybind11 2.10 has a bug relating to binding enums.
+    "pybind11>=2.9,!=2.10",
     "PyYAML",
 ]
 build-backend = "setuptools.build_meta"

lib/Bindings/Python/setup.py

@@ -6,9 +6,9 @@
 # Note that this includes a relatively large build of LLVM (~2400 C++ files)
 # and can take a considerable amount of time, especially with defaults.
 # To install:
-#   pip install . --use-feature=in-tree-build
+#   pip install .
 # To build a wheel:
-#   pip wheel . --use-feature=in-tree-build
+#   pip wheel .
 #
 # It is recommended to build with Ninja and ccache. To do so, set environment
 # variables by prefixing to above invocations: