Remove PyYAML dependency from Python bindings. (iree-org#18262)

Keeping the list of dependencies small will make it easier to depend on
us. Installing `iree-compiler` and `iree-runtime` brings these packages
along:
```
Installing collected packages: mpmath, sympy, PyYAML, numpy, iree-runtime, iree-compiler
Successfully installed PyYAML-6.0.2 iree-compiler-20240816.987 iree-runtime-20240816.987 mpmath-1.3.0 numpy-2.0.1 sympy-1.13.2
```

Unless LLVM/MLIR somehow needs PyYAML (e.g. for linalg opdsl generators
/ tests), I think we can drop it now. `git log -S pyyaml` points to only
these commits:
iree-org@dd787a7,
iree-org@3149b6d.

* PyYAML is still used by
[`build_tools/github_actions/configure_ci.py`](https://github.com/iree-org/iree/blob/main/build_tools/github_actions/configure_ci.py)
and
[`build_tools/github_actions/configure_ci_test.py`](https://github.com/iree-org/iree/blob/main/build_tools/github_actions/configure_ci_test.py).
I just turned off that test in CI. We could install PyYAML (via a
`test_dependencies.txt`) to keep running it, but I think we should focus
on just what the core project truly needs.
* `build_tools/testing/gen_test_matrix.py` hasn't been used in a while
and that sort of test generator should now live in an external
repository like https://github.com/iree-org/iree-test-suites

CMakeLists.txt

@@ -1000,12 +1000,6 @@ endif()
 set(IREE_PUBLIC_INCLUDE_DIRS "${IREE_COMMON_INCLUDE_DIRS}"
     CACHE INTERNAL "IREE: Include Directories" FORCE)
 
-#-------------------------------------------------------------------------------
-# IREE build tools
-#-------------------------------------------------------------------------------
-
-add_subdirectory(build_tools/github_actions)
-
 #-------------------------------------------------------------------------------
 # Optional features
 #-------------------------------------------------------------------------------

build_tools/cmake/iree_python.cmake

@@ -178,38 +178,3 @@ function(iree_py_test)
       ${_RULE_TIMEOUT}
   )
 endfunction()
-
-# iree_build_tools_py_test()
-#
-# CMake function to test with build_tools python modules.
-#
-# Parameters:
-# NAME: name of test
-# SRC: Test source file
-# ARGS: Command line arguments to the Python source file.
-# LABELS: Additional labels to apply to the test. The package path is added
-#     automatically.
-# PACKAGE_DIRS: Additional python module paths.
-function(iree_build_tools_py_test)
-  cmake_parse_arguments(
-    _RULE
-    ""
-    "NAME;SRC"
-    "ARGS;LABELS;PACKAGE_DIRS"
-    ${ARGN}
-  )
-
-  iree_local_py_test(
-    NAME
-      "${_RULE_NAME}"
-    SRC
-      "${_RULE_SRC}"
-    ARGS
-      ${_RULE_ARGS}
-    LABELS
-      ${_RULE_LABELS}
-    PACKAGE_DIRS
-      ${_RULE_PACKAGE_DIRS}
-      "${IREE_ROOT_DIR}/build_tools/python"
-  )
-endfunction()

build_tools/github_actions/ci_requirements.txt

@@ -2,4 +2,3 @@
 # Ensure a recent cmake
 cmake>=3.18.4
 ninja
-PyYAML>=5.4.1

build_tools/python_deploy/README.md

@@ -23,7 +23,7 @@ Python 3.10.4
 # Option A: Build like a normal dev setup (i.e. if allergic to Python
 # packaging and to triage issues that do not implicate that).
 [root@c8f6d0041d79 ]# cd /work/iree
-[root@c8f6d0041d79 iree]# pip install wheel cmake ninja pybind11 PyYAML numpy
+[root@c8f6d0041d79 iree]# pip install wheel cmake ninja pybind11 numpy
 [root@c8f6d0041d79 iree]# cmake -GNinja -B ../iree-build/ -S . -DCMAKE_BUILD_TYPE=Release -DIREE_BUILD_PYTHON_BINDINGS=ON
 [root@c8f6d0041d79 iree]# cd ../iree-build/
 [root@c8f6d0041d79 iree-build]# ninja