chore: remove meaningless comparison

[e-kwsm]

$ faber --builddir=build cxx.name=clang++
…
clangxx.compile src.object/function.o
./src/object/function.cpp:164:42: warning: result of comparison of constant 9223372036854775807 with expression of type 'unsigned int' >
  164 |                         assert(max_arity <= static_cast<std::size_t>(ssize_t_max));
      |                                ~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/assert.h:100:27: note: expanded from macro 'assert'
  100 |      (static_cast <bool> (expr)                                         \
      |                           ^~~~
1 warning generated.
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