Fix hardcoded libjpeg

This is reduntant after libjpeg was added to pkg-config in fa87a16
Fixes #153

configure

@@ -36,7 +36,7 @@ if [ "$INCLUDE_DIR" ] || [ "$LIB_DIR" ]; then
 elif [ "$PKGCONFIG_LIBS" ]; then
   echo "Found pkg-config cflags and libs!"
   PKG_CFLAGS=${PKGCONFIG_CFLAGS}
-  PKG_LIBS="${PKGCONFIG_LIBS} -ljpeg"
+  PKG_LIBS="${PKGCONFIG_LIBS}"
 elif [ `uname` = "Darwin" ]; then
   test ! "$CI" && brew --version 2>/dev/null
   if [ $? -eq 0 ]; then