Remove API deprecated in v0.8.0

[lmb]

Remove API that was marked deprecated when we tagged v0.8.0. Generated by checking out the tag and then running:

$ rg -F '// Deprecated: '
syscalls.go
17:// Deprecated: use os.ErrNotExist instead.

prog.go
707:// Deprecated: use link.RawAttachProgram instead.
725:// Deprecated: use link.RawDetachProgram instead.
791:// Deprecated: use ProgramInfo.ID() instead.

link/netns.go
40:// Deprecated: use LoadPinnedLink instead.

link/cgroup.go
61:// Deprecated: use LoadPinnedLink instead.

link/iter.go
63:// Deprecated: use LoadPinnedLink instead.

link/tracing.go
82:// Deprecated: use LoadPinnedLink instead.

map.go
1440:// Deprecated: use MapInfo.ID() instead.

link/link.go
112:// Deprecated: use Info instead.
196:// Deprecated: use LoadPinnedLink instead.