doc: Revert "doc: Add more known-warnings"

This reverts commit 3127d7b which
was forgotten when switching back to breathe from docleaf and  causing
unecessary "here's a warning about something that's not actually
a warning" :)

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

doc/known-warnings.txt

@@ -22,8 +22,3 @@
 .*Duplicate C declaration.*\n.*'\.\. c:.*:: .*struct in_addr.*'.*
 .*Duplicate C declaration.*\n.*'\.\. c:.*:: .*struct in6_addr.*'.*
 .*Duplicate C declaration.*\n.*'\.\. c:.*:: .*struct net_if.*'.*
-
-# Clash with field of nested anonymous struct
-.*Duplicate C declaration.*\n.*'\.\. c:member:: enum *bt_mesh_dfd_upload_phase bt_mesh_dfd_srv.phase'.*
-.*Duplicate C declaration.*\n.*'\.\. c:member:: struct *bt_mesh_blob_xfer bt_mesh_dfu_cli.blob'.*
-.*Duplicate C declaration.*\n.*'\.\. c:member:: struct *net_if *\* net_if_mcast_monitor.iface'.