gh-92584: Remove references to removed _bootsubprocess (#99062)

The _bootsubprocess module was removed in gh-93939
by commit 81dca70.

Author: vstinner

Lib/_aix_support.py

@@ -1,15 +1,9 @@
 """Shared AIX support functions."""
 
+import subprocess
 import sys
 import sysconfig
 
-try:
-    import subprocess
-except ImportError:  # pragma: no cover
-    # _aix_support is used in distutils by setup.py to build C extensions,
-    # before subprocess dependencies like _posixsubprocess are available.
-    import _bootsubprocess as subprocess
-
 
 def _aix_tag(vrtl, bd):
     # type: (List[int], int) -> str

Tools/wasm/wasm_assets.py

@@ -50,7 +50,6 @@
     "xdrlib.py",
     # other platforms
     "_aix_support.py",
-    "_bootsubprocess.py",
     "_osx_support.py",
     # webbrowser
     "antigravity.py",