Remove unused libwarpctc.so link in core.so and libpaddle_fluid.so

[luotao1]

related #7572 (review)
Now both core.so and libpaddle_fluid.so have the link to libwarpctc.so:

$ ldd core.so
        linux-vdso.so.1 =>  (0x00007ffeab6c5000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f49d87aa000)
        libpython2.7.so.1.0 => /home/luotao02/.jumbo/lib/libpython2.7.so.1.0 (0x00007f49d83ec000)
        librt.so.1 => /lib64/librt.so.1 (0x00007f49d81e4000)
        libwarpctc.so => /home/luotao02/.jumbo/lib/libwarpctc.so (0x00007f49d7fdf000)
...

$ldd /home/luotao02/PaddleRoot/lib/libpaddle_fluid.so
        linux-vdso.so.1 =>  (0x00007ffd6e6e5000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fbc314e6000)
        libwarpctc.so => /home/luotao02/.jumbo/lib/libwarpctc.so (0x00007fbc312e2000)
...

It will cause following error when use libpaddle_fluid.so

$ ../run.sh 
./example: error while loading shared libraries: libwarpctc.so: cannot open shared object file: No such file or directory

However, as libwarpctc.so is dynamic loaded, it should not be linked into core.so and libpaddle_fluid.so.