make: remove redundant 'touch configured'

PREPARE_SRC_VPATH is supposed to prepare the source, so leave
the creation of the 'configured' file to the actual Makefile target.

Cherry picked from: jellyfin@6fb7311

Author: dmitrylyzo

functions.mk

@@ -21,7 +21,6 @@ endef
 define PREPARE_SRC_VPATH
 	rm -rf build/lib/$(1)
 	mkdir -p build/lib/$(1)
-	touch build/lib/$(1)/configured
 endef
 
 # All projects we build have autogen.sh, otherwise we could also fallback to `autoreconf -ivf .`