build: Remove 'sync-descriptions' target.

This target predates 'guix lint'.  Nowadays it makes little sense to run
it upon 'make dist'.

* Makefile.am (sync-descriptions): Remove.
(dist-hook, .PHONY): Remove reference to 'sync-descriptions'.

Makefile.am

@@ -510,15 +510,11 @@ guix-binary.%.tar.xz:
 	cp "$$tarball" "$@.tmp" ; mv "$@.tmp" "$@"
 
 
-dist-hook: sync-descriptions gen-ChangeLog gen-AUTHORS
+dist-hook: gen-ChangeLog gen-AUTHORS
 dist-hook: assert-no-store-file-names
 
 distcheck-hook: assert-binaries-available assert-final-inputs-self-contained
 
-sync-descriptions:
-	$(AM_V_at)GUIX_PACKAGE_PATH= \
-	 $(top_builddir)/pre-inst-env guix lint --checkers=gnu-description
-
 gen-ChangeLog:
 	$(AM_V_GEN)if test -d .git; then		\
 	  $(top_srcdir)/build-aux/gitlog-to-changelog	\
@@ -566,7 +562,7 @@ hydra-jobs.scm: $(GOBJECTS)
 	  "$(top_srcdir)/build-aux/hydra/gnu-system.scm" > "$@.tmp"
 	$(AM_V_at)mv "$@.tmp" "$@"
 
-.PHONY: sync-descriptions gen-ChangeLog gen-AUTHORS clean-go make-go
+.PHONY: gen-ChangeLog gen-AUTHORS clean-go make-go
 .PHONY: assert-no-store-file-names assert-binaries-available
 .PHONY: assert-final-inputs-self-contained