Revert "validate: fix up gir namespace and symbol prefix"

This reverts commit b73e8161.

Part-of: <gstreamer/gst-devtools!214>

validate/gst/validate/meson.build

@@ -82,8 +82,8 @@ if build_gir
             sources : gstvalidate_sources + gstvalidate_headers + gst_validate_enums,
             nsversion : '1.0',
             namespace : 'GstValidate',
-            symbol_prefix : 'gst',
-            identifier_prefix : 'Gst',
+            symbol_prefix : 'gst_validate',
+            identifier_prefix : 'GstValidate',
             export_packages : 'gst-validate-' + apiversion,
             includes : ['GObject-2.0',
                         'GLib-2.0',