[DOCS] Remove 8.x refs (#82580) (#82582)

Removes 8.x refs from the snapshot compatibility matrix.

(cherry picked from commit 2dcf6b3)

docs/reference/snapshot-restore/index.asciidoc

@@ -72,15 +72,15 @@ index or a data stream's backing indices. This means that snapshots can only be
 The following table indicates snapshot compatibility between versions. The first column denotes the base version that you can restore snapshots from.
 
 // tag::snapshot-compatibility-matrix[]
-[cols="6"]
+[cols="5"]
 |===
-| 5+^h| Cluster version
-^h| Snapshot version ^| 2.x ^| 5.x ^| 6.x ^| 7.x ^| 8.x
-^| *1.x* -> ^|{yes-icon} ^|{no-icon}  ^|{no-icon}  ^|{no-icon}  ^|{no-icon}
-^| *2.x* -> ^|{yes-icon} ^|{yes-icon} ^|{no-icon}  ^|{no-icon}  ^|{no-icon}
-^| *5.x* -> ^|{no-icon}  ^|{yes-icon} ^|{yes-icon} ^|{no-icon}  ^|{no-icon}
-^| *6.x* -> ^|{no-icon}  ^|{no-icon}  ^|{yes-icon} ^|{yes-icon} ^|{no-icon}
-^| *7.x* -> ^|{no-icon}  ^|{no-icon}  ^|{no-icon}  ^|{yes-icon} ^|{yes-icon}
+| 4+^h| Cluster version
+^h| Snapshot version ^| 2.x ^| 5.x ^| 6.x ^| 7.x
+^| *1.x* -> ^|{yes-icon} ^|{no-icon}  ^|{no-icon}  ^|{no-icon}
+^| *2.x* -> ^|{yes-icon} ^|{yes-icon} ^|{no-icon}  ^|{no-icon}
+^| *5.x* -> ^|{no-icon}  ^|{yes-icon} ^|{yes-icon} ^|{no-icon}
+^| *6.x* -> ^|{no-icon}  ^|{no-icon}  ^|{yes-icon} ^|{yes-icon}
+^| *7.x* -> ^|{no-icon}  ^|{no-icon}  ^|{no-icon}  ^|{yes-icon}
 |===
 // end::snapshot-compatibility-matrix[]