Removed virtualenv from depot_tools

bootstrap/virtualenv/virtualenv_embedded/activate_this.py

-"""By using execfile(this_file, dict(__file__=this_file)) you will
-activate this virtualenv environment.
-
-This can be used when you must use an existing Python interpreter, not
-the virtualenv bin/python
-"""
-
-try:
-    __file__
-except NameError:
-    raise AssertionError(
-        "You must run this like execfile('path/to/activate_this.py', dict(__file__='path/to/activate_this.py'))")
-import sys
-import os
-
-old_os_path = os.environ.get('PATH', '')
-os.environ['PATH'] = os.path.dirname(os.path.abspath(__file__)) + os.pathsep + old_os_path
-base = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-if sys.platform == 'win32':
-    site_packages = os.path.join(base, 'Lib', 'site-packages')
-else:
-    site_packages = os.path.join(base, 'lib', 'python%s' % sys.version[:3], 'site-packages')
-prev_sys_path = list(sys.path)
-import site
-site.addsitedir(site_packages)
-sys.real_prefix = sys.prefix
-sys.prefix = base
-# Move the added items to the front of the path:
-new_sys_path = []
-for item in list(sys.path):
-    if item not in prev_sys_path:
-        new_sys_path.append(item)
-        sys.path.remove(item)
-sys.path[:0] = new_sys_path