[PATCH doc/rcu 1/2] doc: Fix RCU's docbook options

Commit 764f80798b95 ("doc: Add RCU files to docbook-generation files") added :external: options for RCU source files in the file Documentation/core-api/kernel-api.rst. However, this now means nothing, so this commit removes them. Reported-by: Randy Dunlap Reported-by:

[PATCH doc/rcu 1/2] doc: Fix RCU's docbook options

Commit 764f80798b95 ("doc: Add RCU files to docbook-generation files") added :external: options for RCU source files in the file Documentation/core-api/kernel-api.rst. However, this now means nothing, so this commit removes them. Reported-by: Randy Dunlap Reported-by: