Here is a very short blog about all the deprecated database initialization parameters in 12c.  It is sometime becomes essential to be familiar with those database features and init. parameters that are either de-supported or deprecated in a new release of Oracle database before proceeding with the upgrade. This is because, some of the legacy applications upgrade decision either directly or in-directly depends on those changes.
To obtain a list of deprecated database parameter in 12c, use the following SQL statement:

SQL> SELECT name from v$parameter WHERE isdeprecated = 'TRUE' ORDER BY name;
 
Here is the list:
 
active_instance_count
background_dump_dest
buffer_pool_keep
buffer_pool_recycle
commit_write
cursor_space_for_time
fast_start_io_target
global_context_pool_size
instance_groups
lock_name_space
log_archive_local_first
log_archive_start
max_enabled_roles
parallel_automatic_tuning
parallel_io_cap_enabled
parallel_server
parallel_server_instances
plsql_v2_compatibility
remote_os_authent
resource_manager_cpu_allocation
sec_case_sensitive_logon
serial_reuse
sql_trace
standby_archive_dest
user_dump_dest
 
I am little bit surprised to see the sec_case_sensitive_logon parameter in the list.