[PATCH] config: Remove unnecessary setting/unsetting of prefix in profiles

[Frank Ch. Eigler]

Hi -

> In both profile.csh.in and profile.sh.in we set and then unset
> prefix, but never use it.

It is used, because the autoconf @sysconfdir@ macro expands to a
string like "$prefix/...", which requires the shell variable $prefix
to be set.

- FChE