ENH: Remove superfluous IMMEDIATE option from CMake CONFIGURE_FILE

In CMake 2.0 and higher (since 2005), the IMMEDIATE option to
CONFIGURE_FILE is implicit:
http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=c9cc368a

Change-Id: I60e48f767d33e0a364dfc9cafd9821836b2f3f43
Merge topic 'CMake-Immediate' into master

1f965eec ENH: Remove superfluous IMMEDIATE option from CMake CONFIGURE_FILE