[editorial] specification/README: adjust Hugo front-matter linkTitle …

…field (#3481)

- Adjusts linkTitle
- Contributes to
open-telemetry/opentelemetry.io#2642
- Was originally:
- Drops linkTitle because it is auto-generated since
open-telemetry/opentelemetry.io#2666
- Contributes to
open-telemetry/opentelemetry.io#2387

Co-authored-by: Reiley Yang <reyang@microsoft.com>

specification/README.md

@@ -1,5 +1,5 @@
 <!--- Hugo front matter used to generate the website version of this page:
-linkTitle: Specification
+linkTitle: OTel spec
 no_list: true
 cascade:
   body_class: otel-docs-spec