Revert "Ruby: Use rb prefix in diagnostic IDs for consistency with queries"

This reverts commit a6509c7.

Author: henrymercer

ruby/extractor/src/diagnostics.rs

@@ -93,7 +93,7 @@ impl LogWriter {
         DiagnosticMessage {
             timestamp: chrono::Utc::now(),
             source: Source {
-                id: format!("rb/{}", id),
+                id: format!("{}/{}", self.extractor, id),
                 name: name.to_owned(),
                 extractor_name: Some(self.extractor.to_owned()),
             },

ruby/ql/integration-tests/all-platforms/diagnostics/syntax-error/diagnostics.expected

@@ -14,7 +14,7 @@
   "severity": "warning",
   "source": {
     "extractorName": "ruby",
-    "id": "rb/parse-error",
+    "id": "ruby/parse-error",
     "name": "Parse error"
   },
   "visibility": {
@@ -37,7 +37,7 @@
   "severity": "warning",
   "source": {
     "extractorName": "ruby",
-    "id": "rb/parse-error",
+    "id": "ruby/parse-error",
     "name": "Parse error"
   },
   "visibility": {

ruby/ql/integration-tests/all-platforms/diagnostics/unknown-encoding/diagnostics.expected

@@ -10,7 +10,7 @@
   "severity": "warning",
   "source": {
     "extractorName": "ruby",
-    "id": "rb/unknown-character-encoding",
+    "id": "ruby/unknown-character-encoding",
     "name": "Unknown character encoding"
   },
   "visibility": {