Pass a pointer to user_env in to the init_session policy plugin

function so session setup can modify the user environment as needed.
For PAM authentication, merge the PAM environment with the user
environment at init_session time.  We no longer need to swap in the
user_env for environ during session init, nor do we need to disable
the env hooks at init_session time.

src/sudo.h

@@ -231,7 +231,6 @@ int process_hooks_getenv(const char *name, char **val);
 int process_hooks_setenv(const char *name, const char *value, int overwrite);
 int process_hooks_putenv(char *string);
 int process_hooks_unsetenv(const char *name);
-void deregister_env_hooks(void);
 
 /* interfaces.c */
 int get_net_ifs(char **addrinfo);