Remove unused _find_cmd

It was replaced with shutil/py3compat.which in f42c9edb152ac392caa39fe9e50373ef0ec42a55

IPython/utils/_process_cli.py

@@ -22,14 +22,6 b' import os'
 from IPython.utils import py3compat
 from ._process_common import arg_split
 
-def _find_cmd(cmd):
-    """Find the full path to a command using which."""
-    paths = System.Environment.GetEnvironmentVariable("PATH").Split(os.pathsep)
-    for path in paths:
-        filename = os.path.join(path, cmd)
-        if System.IO.File.Exists(filename):
-            return py3compat.decode(filename)
-    raise OSError("command %r not found" % cmd)
 
 def system(cmd):
     """

IPython/utils/_process_posix.py

@@ -31,14 +31,6 b' from IPython.utils.encoding import DEFAULT_ENCODING'
 # Function definitions
 #-----------------------------------------------------------------------------
 
-def _find_cmd(cmd):
-    """Find the full path to a command using which."""
-
-    path = sp.Popen(['/usr/bin/env', 'which', cmd],
-                    stdout=sp.PIPE, stderr=sp.PIPE).communicate()[0]
-    return py3compat.decode(path)
-
-
 class ProcessHandler(object):
     """Execute subprocesses under the control of pexpect.
     """

IPython/utils/_process_win32.py

@@ -71,27 +71,6 b' class AvoidUNCPath(object):'
             os.chdir(self.path)
 
 
-def _find_cmd(cmd):
-    """Find the full path to a .bat or .exe using the win32api module."""
-    try:
-        from win32api import SearchPath
-    except ImportError as e:
-        raise ImportError('you need to have pywin32 installed for this to work') from e
-    else:
-        PATH = os.environ['PATH']
-        extensions = ['.exe', '.com', '.bat', '.py']
-        path = None
-        for ext in extensions:
-            try:
-                path = SearchPath(PATH, cmd, ext)[0]
-            except:
-                pass
-        if path is None:
-            raise OSError("command %r not found" % cmd)
-        else:
-            return path
-
-
 def _system_body(p):
     """Callback for _system."""
     enc = DEFAULT_ENCODING