Eliminates the sentence about $*REPO

Refs #502

Author: JJ

doc/Language/modules-core.pod6

@@ -4,16 +4,17 @@
 
 =SUBTITLE Core modules that may be useful to module authors
 
-The Rakudo implementation has a few modules included you may want to use. The following is a
-list of them, along with links to their source code.
+The Rakudo implementation has a few modules included you may want to use. The
+following is a list of them, along with links to their source code.
 
 =head2 C<CompUnit::*> modules and Roles
 X<|CompUnit (Rakudo classes)>
 
-These modules are mostly used by distribution build tools.
+These modules are mostly used by distribution build tools, and are not intended
+to be used (at least until version 6.c) by the final user.
 
 =item L«C<CompUnit::Repository::Staging>|https://github.com/rakudo/rakudo/blob/master/lib/CompUnit/Repository/Staging.pm6».
-=item L<C<CompUnit::Repository::(FileSystem|Installation|AbsolutePath|Unknown|NQP|Perl6|RepositoryRegistry)>|https://github.com/rakudo/rakudo/blob/master/src/core/CompUnit/RepositoryRegistry.pm6>. The L<C<$*REPO>|/language/variables#index-entry-%24*REPO> dynamic variable will be instantiated to C<CompUnit::Repository::Installation> if the program is run from the repository main directory, C<CompUnit::Repository::FileSystem> otherwise.
+=item L<C<CompUnit::Repository::(FileSystem|Installation|AbsolutePath|Unknown|NQP|Perl6|RepositoryRegistry)>|https://github.com/rakudo/rakudo/blob/master/src/core/CompUnit/RepositoryRegistry.pm6>.
 
 =head2 C<NativeCall> modules