pkg-config shouldn't add libsrtp2.so to the link flags

```
$ pkg-config --libs jrtplib
-L/usr/local/lib -ljrtp /usr/local/lib/libsrtp2.so 
```

Only binaries that immediately use the library should be linked with it. So ```/usr/local/lib/libjrtp.so.3.11.1``` should be linked with ```/usr/local/lib/libsrtp2.so```, but binaries that use ```/usr/local/lib/libjrtp.so``` shouldn't be linked with it.
