sysutils/symon: Fix build on 32 bit machines

symonnet.c:76:9: error: comparison of integers of different signs: 'ssize_t' (aka 'int') and 'u_int32_t' (aka 'unsigned int') [-Werror,-Wsign-compare]"

While here, also remove the unneccesary dependency on "groff".

PR: 293667