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: I1cf964bc280fc66261fc308571f9c00c5ac8da8b
Merge topic 'CMake-Immediate'

55cb13c ENH: Remove superfluous IMMEDIATE option from CMake CONFIGURE_FILE