Fix description of filter flag in prune commands

The "-f" flag is an alias for --force, not --filter (as correctly stated at the top of each documents). The system_prune.md didn't have this error.

Signed-off-by: Mateusz Major <apkd@users.noreply.github.com>

docs/reference/commandline/container_prune.md

@@ -48,7 +48,7 @@ Total reclaimed space: 212 B
 
 ### Filtering
 
-The filtering flag (`-f` or `--filter`) format is of "key=value". If there is more
+The filtering flag (`--filter`) format is of "key=value". If there is more
 than one filter, then pass multiple flags (e.g., `--filter "foo=bar" --filter "bif=baz"`)
 
 The currently supported filters are:

docs/reference/commandline/image_prune.md

@@ -70,7 +70,7 @@ Total reclaimed space: 16.43 MB
 
 ### Filtering
 
-The filtering flag (`-f` or `--filter`) format is of "key=value". If there is more
+The filtering flag (`--filter`) format is of "key=value". If there is more
 than one filter, then pass multiple flags (e.g., `--filter "foo=bar" --filter "bif=baz"`)
 
 The currently supported filters are:

docs/reference/commandline/network_prune.md

@@ -36,7 +36,7 @@ n2
 
 ### Filtering
 
-The filtering flag (`-f` or `--filter`) format is of "key=value". If there is more
+The filtering flag (`--filter`) format is of "key=value". If there is more
 than one filter, then pass multiple flags (e.g., `--filter "foo=bar" --filter "bif=baz"`)
 
 The currently supported filters are:

docs/reference/commandline/volume_prune.md

@@ -46,7 +46,7 @@ Total reclaimed space: 36 B
 
 ## Filtering
 
-The filtering flag (`-f` or `--filter`) format is of "key=value". If there is more
+The filtering flag (`--filter`) format is of "key=value". If there is more
 than one filter, then pass multiple flags (e.g., `--filter "foo=bar" --filter "bif=baz"`)
 
 The currently supported filters are: