removed internal or local setting /home/y/lib in QMAKE_RPATH

/home/y/lib must be an internal or developers' specific local setting - users normally would not have such a directory, therefore suggesting to delete the unnecessary setting.

Partial link command on Ubuntu 13.10 with the current setting:
make[1]: Entering directory `[...]/tpjs/src'
g++ -Wl,-O1 -Wl,-rpath,/home/y/lib -o ../bin/phantomjs phantom.o callback.o webpage.o [...]