Remove vendor Wifi and BT entries from fs_config.cpp

Their capability bits are now specified in their associated init .rc
file, which is the proper place for this to be done.

A notice is added to guide developers away from using android_files to
give services Linux capabilities and to guide them away from adding
vendor/ entries.

Bug: 74554159
Test: BT, Wifi, Tethering work on walleye
Change-Id: I13c425d022b4f5c217587cdf601884ef44650ac7