security: fix build

Regression introduced in commit 18338388.

* src/libvirt_private.syms (security_manager.h): Drop deleted
symbol. Detected by build-bot.

src/libvirt_private.syms

@@ -908,7 +908,6 @@ virSecurityManagerSetDaemonSocketLabel;
 virSecurityManagerSetImageFDLabel;
 virSecurityManagerSetImageLabel;
 virSecurityManagerSetHostdevLabel;
-virSecurityManagerSetProcessFDLabel;
 virSecurityManagerSetProcessLabel;
 virSecurityManagerSetSavedStateLabel;
 virSecurityManagerSetSocketLabel;