libusb-1.0 is already part of RTLSDR_PC_LIBS

--- librtlsdr.pc.in.orig	2014-07-11 08:56:42.640078065 +0000
+++ librtlsdr.pc.in	2014-07-11 08:56:57.487076496 +0000
@@ -7,5 +7,5 @@
 Description: C Utility Library
 Version: @VERSION@
 Cflags: -I${includedir}/ @RTLSDR_PC_CFLAGS@
-Libs: -L${libdir} -lrtlsdr -lusb-1.0
+Libs: -L${libdir} -lrtlsdr
 Libs.private: @RTLSDR_PC_LIBS@