DOC: configuration: fix set-dst in actions keywords matrix

DOC: configuration: fix set-dst in actions keywords matrix

Since d54e8f8107 ("DOC: config: reorganize actions into their own section")
dconv-generated shortlink for "set-dst" in actions keywords matrix is
broken.

This is due to trailing "<expr>" which should not be specified in the
matrix, but only in the actual keyword prototype and description.

This should be backported in 2.9 with d54e8f8107.

(cherry picked from commit 62ef7966f0312e31e6fb8fc9e572e0e907e28558)
Signed-off-by: Willy Tarreau <w@1wt.eu>