[scripts/fx] Remove outdated comment

The usage syntax specifies that only one of --config and --dir is allowed.
No point in elaborating further

Tested: fx help
Change-Id: I9cdc5ec89df6d55390ecb73e097f465c1de1ea7d
diff --git a/scripts/fx b/scripts/fx
index acf5242..63d7f93 100755
--- a/scripts/fx
+++ b/scripts/fx
@@ -96,7 +96,6 @@
                         file determines which build directory (and therefore
                         build configuration) is used by COMMAND.
   --dir=BUILD_DIR       Path to the build directory to use when running COMMAND.
-                        If specified, FILE is ignored.
   -d=DEVICE_NAME        Target a specific device. DEVICE_NAME may be a Fuchsia
                         device name. Note: "fx set-device" can be used to set a
                         default DEVICE_NAME for a BUILD_DIR.