Remove SO_NAME_MAX_PATH_SIZE limit from core solib code

solib_map_sections errors out if the library file name is longer than
SO_NAME_MAX_PATH_SIZE.

solib::so_name and solib::so_original_name used to be arrays of
SO_NAME_MAX_PATH_SIZE size, so that check made sense then.

However, since commit 98107b0b ("gdb: make
so_list::{so_original_name,so_name} std::strings") those fields are of
std::string type, so there's really no need for the limit.

This commit simply removes the length limit check.

Approved-By: John Baldwin <jhb@FreeBSD.org>
Change-Id: I2ec676b231cd18ae900c61c5caea461f47e989e6