dyndbg-docs: eschew file /full/path query in docs

Regarding:
commit 2b67831 ("dynamic_debug: add trim_prefix() to provide source-root relative paths")
commit a73619a ("kbuild: use -fmacro-prefix-map to make __FILE__ a relative path")

2nd commit broke dynamic-debug's "file $fullpath" query form, but
nobody noticed because 1st commit had trimmed prefixes from
control-file output, so the click-copy-pasting of fullpaths into new
queries had ceased; that query form became unused.

Removing the function is cleanest, but it could be useful in
old-compiler corner cases, where __FILE__ still has /full/path,
and it safely does nothing otherwize.

So instead, quietly deprecate "file /full/path" query form, by
removing all /full/paths examples in the docs.  I skipped adding a
back-compat note.

Acked-by: <jbaron@akamai.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20200719231058.1586423-2-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/admin-guide/dynamic-debug-howto.rst

@@ -70,10 +70,10 @@ statements via::
 
   nullarbor:~ # cat <debugfs>/dynamic_debug/control
   # filename:lineno [module]function flags format
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup =_ "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline       : %d\012"
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth         : %d\012"
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests     : %d\012"
+  net/sunrpc/svc_rdma.c:323 [svcxprt_rdma]svc_rdma_cleanup =_ "SVCRDMA Module Removed, deregister RPC RDMA transport\012"
+  net/sunrpc/svc_rdma.c:341 [svcxprt_rdma]svc_rdma_init =_ "\011max_inline       : %d\012"
+  net/sunrpc/svc_rdma.c:340 [svcxprt_rdma]svc_rdma_init =_ "\011sq_depth         : %d\012"
+  net/sunrpc/svc_rdma.c:338 [svcxprt_rdma]svc_rdma_init =_ "\011max_requests     : %d\012"
   ...
 
 
@@ -93,7 +93,7 @@ the debug statement callsites with any non-default flags::
 
   nullarbor:~ # awk '$3 != "=_"' <debugfs>/dynamic_debug/control
   # filename:lineno [module]function flags format
-  /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012"
+  net/sunrpc/svcsock.c:1603 [sunrpc]svc_send p "svc_process: st_sendto returned %d\012"
 
 Command Language Reference
 ==========================
@@ -166,13 +166,12 @@ func
 	func svc_tcp_accept
 
 file
-    The given string is compared against either the full pathname, the
-    src-root relative pathname, or the basename of the source file of
-    each callsite.  Examples::
+    The given string is compared against either the src-root relative
+    pathname, or the basename of the source file of each callsite.
+    Examples::
 
 	file svcsock.c
-	file kernel/freezer.c
-	file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
+	file kernel/freezer.c	# ie column 1 of control file
 
 module
     The given string is compared against the module name