Remove redundant insert method in serialize.

This seems to cause problems on recent clang, and looks totally
redundant and unused.

The const_iterator version is identical to the vector::const_iterator
one (which is a typedef thereof). Marking it private (instead of
removing) compiles fine, so this version is effectively unused even.
Checkpoints online.
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Testnet port value of 119985 is too long for 'unsigned short', changed
to 'unsigned long' to compensate. Probably doesn't matter as testnet
is disabled.  This fixes the warning, though.

      src/protocol.h:21:22: warning: implicit conversion from 'int' to
          'unsigned short' changes value from 119985 to 54449
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