core: Remove additional symbols.

Remove symbols that are depreacated and replaced:
* ast_channel_datastore_alloc
* ast_channel_datastore_free
* ast_channel_cmpwhentohangup
* ast_channel_setwhentohangup
* config_text_file_save
* devstate2str
* ast_device_state_changed
* ast_device_state_changed_literal
* ast_verbose_get_by_module

Remove unused symbols:
* channelreloadreason2txt (last used in Asterisk 12).

Remove unused ast_options flags:
* AST_OPT_FLAG_END_CDR_BEFORE_H_EXTEN / ast_opt_end_cdr_before_h_exten
* AST_OPT_FLAG_VERBOSE_MODULE / ast_opt_verb_module
* AST_OPT_FLAG_INITIATED_SECONDS

Change-Id: I841255995d195f8efc1ed47af9c7a2f131c08645