docs: exclude dummy.c sources

They are empty sources used to build OCaml-only targets using automake,
so there is no documentation to extract.

Makefile.am

@@ -320,6 +320,7 @@ docs/C_SOURCE_FILES: configure.ac
 	grep -v -E '/(guestfs|rc)_protocol\.' | \
 	grep -v -E '.*/errnostring\.' | \
 	grep -v -E '.*-gperf\.' | \
+	grep -v -E '/dummy.c$$' | \
 	LC_ALL=C sort -u > $@-t
 	mv $@-t $@
 

docs/C_SOURCE_FILES

@@ -12,21 +12,14 @@ cat/ls.c
 cat/tail.c
 common/edit/file-edit.c
 common/edit/file-edit.h
-common/mlcustomize/dummy.c
-common/mlgettext/dummy.c
-common/mlpcre/dummy.c
 common/mlpcre/pcre-c.c
 common/mlprogress/progress-c.c
-common/mlstdutils/dummy.c
 common/mltools/JSON_parser-c.c
-common/mltools/dummy.c
 common/mltools/getopt-c.c
 common/mltools/tools_utils-c.c
 common/mltools/uri-c.c
 common/mlutils/c_utils-c.c
-common/mlutils/dummy.c
 common/mlutils/unix_utils-c.c
-common/mlvisit/dummy.c
 common/mlvisit/visit-c.c
 common/mlxml/xml-c.c
 common/options/config.c
@@ -67,7 +60,6 @@ common/visit/visit.h
 common/windows/windows.c
 common/windows/windows.h
 customize/crypt-c.c
-customize/dummy.c
 customize/perl_edit-c.c
 daemon/9p.c
 daemon/acl.c
@@ -202,7 +194,6 @@ df/df.c
 df/main.c
 df/output.c
 df/virt-df.h
-dib/dummy.c
 diff/diff.c
 edit/edit.c
 erlang/actions-0.c
@@ -270,7 +261,6 @@ fuse/guestunmount.c
 fuse/test-fuse.c
 fuse/test-guestmount-fd.c
 fuse/test-guestunmount-fd.c
-get-kernel/dummy.c
 inspector/inspector.c
 java/actions-0.c
 java/actions-1.c
@@ -370,7 +360,6 @@ rescue/escape.c
 rescue/rescue.c
 rescue/rescue.h
 rescue/suggest.c
-resize/dummy.c
 ruby/ext/guestfs/actions-0.c
 ruby/ext/guestfs/actions-1.c
 ruby/ext/guestfs/actions-2.c
@@ -381,6 +370,4 @@ ruby/ext/guestfs/actions-6.c
 ruby/ext/guestfs/actions.h
 ruby/ext/guestfs/handle.c
 ruby/ext/guestfs/module.c
-sparsify/dummy.c
-sysprep/dummy.c
 test-tool/test-tool.c