Unix: Remove now unnecessary I/O defines, cleanup

- `LIBC_FILEIO_ENABLED` wasn't defined anywhere, even in _other platforms_.
- `NO_NETWORK` is also never defined. It probably isn't enough anyway to
  disable network APIs in the current codebase.
- `UNIX_SOCKET_UNAVAILABLE` is never defined in this code but used by some
  other platforms, clarify that.
- `NO_STATVFS` can be removed as Android supports it since API level 19,
  which is our current min SDK level. It's also only used for
  `DirAccessUnix::get_space_left()` which is anyway overridden by
  `DirAccessJAndroid::get_space_left()` so it shouldn't make a difference.
  * Fixed documentation for `DirAccess.get_space_left()`.
- `NO_FCNTL` is likely also a remnant of early Android days, in current NDK
  r23 it seems to be available. Also cleaned up unused `fcntl.h` includes.
- `NO_ALLOCA` is never defined, and we use alloca in many places now.

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/unix/os_unix.h b/drivers/unix/os_unix.h
index b35f161524..ce81ca0aca 100644
--- a/drivers/unix/os_unix.h
+++ b/drivers/unix/os_unix.h
@@ -53,7 +53,7 @@ public:
 
 	virtual String get_stdin_string(bool p_block) override;
 
-	virtual Error get_entropy(uint8_t *r_buffer, int p_bytes) override; // Should return cryptographycally-safe random bytes.
+	virtual Error get_entropy(uint8_t *r_buffer, int p_bytes) override;
 
 	virtual Error open_dynamic_library(const String p_path, void *&p_library_handle, bool p_also_set_library_path = false, String *r_resolved_path = nullptr) override;
 	virtual Error close_dynamic_library(void *p_library_handle) override;