fix transitive linking for x-builds

-rpath does *not* imply -rpath-link when x-building:
ld(1): "Searching -rpath in this way is only supported by native linkers
and cross linkers which have been configured with the --with-sysroot
option."

it doesn't hurt to have the "excess" -rpath-link for native builds, so
just remove the cleanup.

Change-Id: Ic39c1f4d6c2e3770d43a5ed3e56cf89a146edf85
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

mkspecs/features/qt_functions.prf

@@ -195,7 +195,6 @@ defineTest(qtAddRpathLink) {
     for(dep, privdep): \
         rpaths += $$eval(QT.$${dep}.libs)
     QMAKE_RPATHLINKDIR *= $$unique(rpaths)
-    QMAKE_RPATHLINKDIR -= $$QMAKE_RPATHDIR   # -rpath implies -rpath-link
     export(QMAKE_RPATHLINKDIR)
 }