update disappearing messages options

[r10s]

• after some discussion in the forum and other channels, we decided to add the option "After 1 Year" (string key autodel_after_1_year) with the value 31536000 (606024*365); see add "After 1 year" option to disappearing messages deltachat-android#3467 for reference implementation

• the stock strings DC_STR_EPHEMERAL_TIMER_1_YEAR_BY_YOU and DC_STR_EPHEMERAL_TIMER_1_YEAR_BY_OTHER needs to be set to ephemeral_timer_1_year_by_you resp. ephemeral_timer_1_year_by_other

• the "1 minute" and "30 minutes" options shall be removed, see drop disappearing messages options 1 and 30 minutes deltachat-android#3897 for reasoning

counterpart of deltachat/deltachat-desktop#5421