Close #20757: return success for skipped pip uninstall

The 3.4rc2 Windows uninstaller would fail if pip had been updated
to a version that didn't match the version installed by ensurepip.
This skip is no longer treated as an error, so an updated pip ends
up being handled like any other pip installed package and is left
alone by the CPython uninstaller.
diff --git a/Lib/ensurepip/__init__.py b/Lib/ensurepip/__init__.py
index f584bdc..7cf6a4b 100644
--- a/Lib/ensurepip/__init__.py
+++ b/Lib/ensurepip/__init__.py
@@ -128,9 +128,10 @@
 
     # If the pip version doesn't match the bundled one, leave it alone
     if pip.__version__ != _PIP_VERSION:
-        msg = ("ensurepip will only uninstall a matching pip "
+        msg = ("ensurepip will only uninstall a matching version "
                "({!r} installed, {!r} bundled)")
-        raise RuntimeError(msg.format(pip.__version__, _PIP_VERSION))
+        print(msg.format(pip.__version__, _PIP_VERSION), file=sys.stderr)
+        return
 
     _require_ssl_for_pip()
     _disable_pip_configuration_settings()