Fix race in check-guile to make needless guile-procedures symlink

* check-guile.in (top_srcdir): Don't try to make guile-procedures.tx, as
this races with multiple checkers, and it's gross.
* meta/uninstalled-env.in (GUILE_DOCSTRINGS_PATH): Instead when
uninstalled, use this variable.
* module/ice-9/documentation.scm (documentation-files): Remove the
current directory from the search path for documentation files; this was
always a hack.  Instead allow GUILE_DOCSTRINGS_PATH to override the
built-in search path.

check-guile.in

@@ -31,11 +31,6 @@ if ! [ -f "$guile" -a -x "$guile" ] ; then
     exit 2
 fi
 
-# documentation searching ignores GUILE_LOAD_PATH.
-if [ ! -f guile-procedures.txt ] ; then
-   @LN_S@ libguile/guile-procedures.txt .
-fi
-
 exec "$guile" \
     --debug \
     -L "$TEST_SUITE_DIR" \