Removes klee_make_symbolic/get_value calls from port I/O operations

This patch removes the klee_make_symbolic and klee_get_value calls
from the port I/O code, and removes these function implements
altogether.  The old approach was not compatible with conconcolic
execution.  This patch removes related code from the KLEE
SpecialFunctionHandler.cpp.

New functionality includes the handleMakeSymbolic and handleGetValue
calls in S2EExecutor, as well as the makeSymbolic and
kleeRead/WriteMemory calls in S2EExecutionState.