output/log: Remove extraneous error message

Issue: 7447

When the output file can't be opened, 2 error messages are displayed
for the same problem. The second message doesn't add value and lacks
context (error reason, e.g., "Permission denied").

Retaining the second message as a debug message.

Without this commit:

Error: logopenfile: Error opening file: "/home/jlucovsky/src/jal/suricata-verify/tests/bug-5198/output/noperms/eve.1.json": Permission denied [SCLogOpenFileFp:util-logopenfile.c:428]
Error: logopenfile: Unable to open slot 1 for file /home/jlucovsky/src/jal/suricata-verify/tests/bug-5198/output/noperms/eve.json [LogFileEnsureExists:util-logopenfile.c:737]
Error: runmodes: unable to initialize sub-module eve-log.stats [RunModeInitializeEveOutput:runmodes.c:692]

With commit:

Error: logopenfile: Error opening file: "/home/jlucovsky/src/jal/suricata-verify/tests/bug-5198/output/noperms/eve.1.json": Permission denied [SCLogOpenFileFp:util-logopenfile.c:428]
Error: runmodes: unable to initialize sub-module eve-log.stats [RunModeInitializeEveOutput:runmodes.c:692]

src/util-logopenfile.c

@@ -733,7 +733,7 @@ LogFileCtx *LogFileEnsureExists(ThreadId thread_id, LogFileCtx *parent_ctx)
             entry->isopen = true;
             ret_ctx = entry->ctx;
         } else {
-            SCLogError(
+            SCLogDebug(
                     "Unable to open slot %d for file %s", entry->slot_number, parent_ctx->filename);
             (void)HashTableRemove(parent_ctx->threads->ht, entry, 0);
         }