Remove Wen's gpg key, separate all keys in different blocks

Wen is no longer a maintainer, so remove his GPG key.

Put all the keys in different PUBLIC KEY BLOCKS, so it's easier to add
or remove them manually.

After the change:
> gpg --show-keys nmstate.gpg
pub   rsa4096 2023-04-20 [SC] [caduca: 2027-04-19]
      48FD6FAE515A77B48436821C8789567B8715CEBC
uid                      Gris Ge <fge@redhat.com>
sub   rsa4096 2023-04-20 [E] [caduca: 2027-04-19]

pub   rsa4096 2023-04-20 [SC]
      2B5F3B2028801E15F57AAA309906C97AA15D984F
uid                      Fernando Fernandez Mancera <ffmancera@riseup.net>
sub   rsa4096 2023-04-20 [E]

pub   rsa2048 2021-06-04 [SC]
      07F9AEC86144386D9576210B66A44781B4EBC2D0
uid                      Íñigo Huguet <ihuguet@redhat.com>
sub   rsa2048 2021-06-04 [E]

pub   rsa4096 2023-11-29 [SC]
      ACFA41513D2854D0A72F55BE9A2C77A85F2D72FE
uid                      Ján Václav <jvaclav@redhat.com>
sub   rsa4096 2023-11-29 [E]

Signed-off-by: Íñigo Huguet <ihuguet@riseup.net>