Share one selection menu; drop dead variant detection and TegraExplorer filter

The variant menu in main.c and the RAM / Hekate-AMS menus in install.c
were three copies of the same input loop; install_menu_select() replaces
them with identical behaviour (D-pad/Vol to move, A/Power to confirm,
Vol+ and Vol- to abort, Capture for screenshots).

source/version.h

@@ -24,8 +24,6 @@ typedef struct {
 // Detect current OmniNX installation status
 omninx_status_t detect_omninx_installation(void);
 
-// Detect which pack variant is present on SD card (first found in fixed order)
-omninx_variant_t detect_pack_variant(void);
 
 // Detect all pack variants present on SD card; returns count, fills out_variants[] (max max_count)
 int detect_present_variants(omninx_variant_t *out_variants, int max_count);