Drop the converters for old data

2.15.0 stored all settings, schedules and pages on the display in the
current formats (old_data_left 0), so only those are read now: settings
version 7, schedule version 4, page format 7. The one-time migrations
(icons from 2.10.0, data from 2.15.0) are removed too. About 9 KB less
flash. CLAUDE.md says how to keep data over a future format change.

Version 2.15.1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/esp32/app.h

@@ -65,15 +65,6 @@ const char *appDeleteIcon(const char *name);
 // the other way around; not for bitmaps that are shown on their own
 const char *appBitmapToIcon(const char *name);
 const char *appIconToBitmap(const char *name);
-// Once: the uploaded bitmaps that only pages use become icons. Call from loop(); returns at
-// once when it is done.
-void appMigrateIcons();
-// Once per boot, after the firmware was marked good (the old firmware can't read the new
-// formats): settings and schedule read in an older layout are stored again, and pages in an
-// older format are rewritten. Call from loop(); returns at once when it is done.
-void appMigrateData();
-// Records still in an older format (-1 until appMigrateData() checked the pages)
-int appOldDataLeft();
 const char *appSavePage(const char *name, const DynamicPage &page);
 const char *appDeletePage(const char *name);
 const char *appSaveFont(const char *name, const uint8_t *data, size_t size);