dump: Drop pointless error_is_set(), DumpState member errp

In qmp_dump_guest_memory(), the error must be clear on entry, and we
always bail out after setting it, directly or via dump_init().
Therefore, both error_is_set() are always false.  Drop them.

DumpState member errp is now write-only.  Drop it, too.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

dump.c

@@ -86,7 +86,6 @@ typedef struct DumpState {
     bool has_filter;
     int64_t begin;
     int64_t length;
-    Error **errp;
 
     uint8_t *note_buf;          /* buffer for notes */
     size_t note_buf_offset;     /* the writing place in note_buf */
@@ -1570,7 +1569,6 @@ static int dump_init(DumpState *s, int fd, bool has_format,
         nr_cpus++;
     }
 
-    s->errp = errp;
     s->fd = fd;
     s->has_filter = has_filter;
     s->begin = begin;
@@ -1780,11 +1778,11 @@ void qmp_dump_guest_memory(bool paging, const char *file, bool has_begin,
     }
 
     if (has_format && format != DUMP_GUEST_MEMORY_FORMAT_ELF) {
-        if (create_kdump_vmcore(s) < 0 && !error_is_set(s->errp)) {
+        if (create_kdump_vmcore(s) < 0) {
             error_set(errp, QERR_IO_ERROR);
         }
     } else {
-        if (create_vmcore(s) < 0 && !error_is_set(s->errp)) {
+        if (create_vmcore(s) < 0) {
             error_set(errp, QERR_IO_ERROR);
         }
     }