meson: remove unnecessary reference to libm

libm is linked into all targets via libqemuutil, no need to specify it
explicitly.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

block/meson.build

@@ -110,7 +110,7 @@ foreach m : [
   [blkio, 'blkio', files('blkio.c')],
   [curl, 'curl', files('curl.c')],
   [glusterfs, 'gluster', files('gluster.c')],
-  [libiscsi, 'iscsi', [files('iscsi.c'), libm]],
+  [libiscsi, 'iscsi', files('iscsi.c')],
   [libnfs, 'nfs', files('nfs.c')],
   [libssh, 'ssh', files('ssh.c')],
   [rbd, 'rbd', files('rbd.c')],