Remove toolchain statement from otelgin example (#6178)

Closes #6170.

Co-authored-by: Robert Pająk <[email protected]>

Author: dmathieu

instrumentation/github.com/gin-gonic/gin/otelgin/example/go.mod

@@ -2,8 +2,6 @@ module go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otel
 
 go 1.22
 
-toolchain go1.23.0
-
 replace (
 	go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin => ../
 	go.opentelemetry.io/contrib/propagators/b3 => ../../../../../../propagators/b3