md25: remove used source files BlockSysIdent.{cpp,hpp}

src/drivers/md25/BlockSysIdent.cpp

-#include "BlockSysIdent.hpp"
-
-BlockSysIdent::BlockSysIdent() :
-	Block(NULL, "SYSID"),
-	_freq(this, "FREQ"),
-	_ampl(this, "AMPL")
-{
-}

src/drivers/md25/BlockSysIdent.hpp

-#include <controllib/block/Block.hpp>
-#include <controllib/block/BlockParam.hpp>
-
-class BlockSysIdent : public control::Block
-{
-public:
-	BlockSysIdent();
-private:
-	BlockParamFloat _freq;
-	BlockParamFloat _ampl;
-};