Don't mention --preserve-test-targets.

Targets are no longer removed by default, so this reference
is unnecessary.

Addresses #2001.


[SVN r53379]

libs/python

@@ -1 +1 @@
-Subproject commit 3ecb3301a21bf907d68c8460f6eff7939627e4bb
+Subproject commit ef53bedd0a74303ef33c990d18bd37528d659426