networkcache: remove invalid signature certificate

Recent versions of OpenSSL refuse to load Romain's key:

  unable to load certificate
  140268475908992:error:0D0E20DE:asn1 encoding routines:c2i_ibuf:illegal zero content:../crypto/asn1/a_int.c:154:
  140268475908992:error:0D08303A:asn1 encoding routines:asn1_template_noexp_d2i:nested asn1 error:../crypto/asn1/tasn_dec.c:609:Field=serialNumber, Type=X509_CINF
  140268475908992:error:0D08303A:asn1 encoding routines:asn1_template_noexp_d2i:nested asn1 error:../crypto/asn1/tasn_dec.c:609:Field=cert_info, Type=X509
  140268475908992:error:0906700D:PEM routines:PEM_ASN1_read_bio:ASN1 lib:../crypto/pem/pem_oth.c:33:

With older versions:

  Certificate:
      Data:
          Version: 1 (0x0)
          Serial Number: 0 (0x0)
      ...
Acked-by: Romain Courteaud <romain@nexedi.com>

stack/slapos.cfg

@@ -200,7 +200,6 @@ download-cache-url = http://download.shacache.org/
 download-dir-url = http://dir.shacache.org/
 
 # signature certificates of the following uploaders.
-#   Romain Courteaud
 #   Sebastien Robin
 #   Kazuhiko Shiozaki
 #   Gabriel Monnerat
@@ -210,19 +209,6 @@ download-dir-url = http://dir.shacache.org/
 #   Ivan Tyagov
 #   Julien Muchembled
 signature-certificate-list =
-  -----BEGIN CERTIFICATE-----
-  MIIB4DCCAUkCADANBgkqhkiG9w0BAQsFADA5MQswCQYDVQQGEwJGUjEZMBcGA1UE
-  CBMQRGVmYXVsdCBQcm92aW5jZTEPMA0GA1UEChMGTmV4ZWRpMB4XDTExMDkxNTA5
-  MDAwMloXDTEyMDkxNTA5MDAwMlowOTELMAkGA1UEBhMCRlIxGTAXBgNVBAgTEERl
-  ZmF1bHQgUHJvdmluY2UxDzANBgNVBAoTBk5leGVkaTCBnzANBgkqhkiG9w0BAQEF
-  AAOBjQAwgYkCgYEApYZv6OstoqNzxG1KI6iE5U4Ts2Xx9lgLeUGAMyfJLyMmRLhw
-  boKOyJ9Xke4dncoBAyNPokUR6iWOcnPHtMvNOsBFZ2f7VA28em3+E1JRYdeNUEtX
-  Z0s3HjcouaNAnPfjFTXHYj4um1wOw2cURSPuU5dpzKBbV+/QCb5DLheynisCAwEA
-  ATANBgkqhkiG9w0BAQsFAAOBgQBCZLbTVdrw3RZlVVMFezSHrhBYKAukTwZrNmJX
-  mHqi2tN8tNo6FX+wmxUUAf3e8R2Ymbdbn2bfbPpcKQ2fG7PuKGvhwMG3BlF9paEC
-  q7jdfWO18Zp/BG7tagz0jmmC4y/8akzHsVlruo2+2du2freE8dK746uoMlXlP93g
-  QUUGLQ==
-  -----END CERTIFICATE-----
   -----BEGIN CERTIFICATE-----
   MIIB8jCCAVugAwIBAgIJAPu2zchZ2BxoMA0GCSqGSIb3DQEBBQUAMBIxEDAOBgNV
   BAMMB3RzeGRldjMwHhcNMTExMDE0MTIxNjIzWhcNMTIxMDEzMTIxNjIzWjASMRAw