[Build] Fix Python linting issues.

The Python linter was complaining about import orders.

rdar://123503470

Author: al45tair

utils/swift_build_support/swift_build_support/products/llvm.py

@@ -11,7 +11,6 @@
 # ----------------------------------------------------------------------------
 
 import os
-import errno
 import shutil
 from platform import system
 

utils/swift_build_support/swift_build_support/targets.py

@@ -8,11 +8,9 @@
 # See https://swift.org/LICENSE.txt for license information
 # See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-import atexit
-import contextlib
 import os
-import platform
 import importlib.resources
+import platform
 
 from . import cmake
 from . import shell