ebpf: really include it only in system emulators

eBPF libraries are being included in user emulators, which is useless and
also breaks --static compilation if a shared library for libbpf is
present in the system.

Reported-by: Alex Bennée <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: bonzini

meson.build

@@ -2300,8 +2300,6 @@ subdir('bsd-user')
 subdir('linux-user')
 subdir('ebpf')
 
-common_ss.add(libbpf)
-
 bsd_user_ss.add(files('gdbstub.c'))
 specific_ss.add_all(when: 'CONFIG_BSD_USER', if_true: bsd_user_ss)