Do not generate code for the init function of chpl__Program

[reviewed by Brad]

While we still need chpl__init_chpl__Program() during compilation, it
is no longer called at runtime, so we do not need to generate any code
for it.  Added the "no codegen" flag to that function and removed the
"export" flag.



git-svn-id: http://svn.code.sf.net/p/chapel/code/trunk@22147 3a8e244f-b0f2-452b-bcba-4c88e055c3ca