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.c

@@ -146,20 +146,6 @@ omninx_status_t detect_omninx_installation(void) {
     return status;
 }
 
-// Detect which pack variant is present on SD card
-omninx_variant_t detect_pack_variant(void) {
-    // Check staging directories (in order of preference)
-    if (file_exists(STAGING_STANDARD)) {
-        return VARIANT_STANDARD;
-    } else if (file_exists(STAGING_LIGHT)) {
-        return VARIANT_LIGHT;
-    } else if (file_exists(STAGING_OC)) {
-        return VARIANT_OC;
-    }
-    
-    return VARIANT_NONE;
-}
-
 // Detect all pack variants present on SD card; returns count, fills out_variants[]
 int detect_present_variants(omninx_variant_t *out_variants, int max_count) {
     int count = 0;