* guix/gexp.scm (gexp-inputs)[add-reference-inputs]: Remove clause for
inputs of the form (PACKAGE OUTPUT).
(gexp->sexp)[reference->sexp]: Likewise.
* tests/gexp.scm ("input list splicing"): Change 'list' to 'gexp-input'
for glibc:debug.
("text-file*"): Likewise for %bootstrap-guile:out.
("input list splicing + gexp-input + ungexp-native-splicing"): Remove,
now redundant.