MFC r291310:

Stop building vers.c in include/ and only build the needed osreldate.h.

Because of how osreldate.h was being built with newvers.sh, which always
spat out a vers.c dependent on SVN or git, the meta mode build was
considering osreldate.h to depend on the current git or SVN index. This
would lead to entire tree rebuilds when modifying git's index. There's
no reason to be generating vers.c here so just skip it.

While here, in mk-osreldate.sh rename PARAM_H to proper PARAMFILE (which
newvers.sh already has a default for) and remove unneeded export.

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