roachtest: delete version/mixed tests

This commit deletes the version/mixed roachtests. These tests
do very little, only testing that upgrades finish. This
is tested by other mixed-version tests, rendering these tests
redundant.

Note that these tests did test upgrades for clusters of size 5,
something we don't do elsewhere. However it isn't worth it to
have a seperate test for this.

Release note: None

Epic: CRDB-19321
Fixes: #110538
Informs: #110528

pkg/cmd/roachtest/tests/BUILD.bazel

@@ -178,7 +178,6 @@ go_library(
         "util_if_local.go",
         "util_load_group.go",
         "validate_system_schema_after_version_upgrade.go",
-        "version.go",
         "versionupgrade.go",
         "ycsb.go",
     ],

pkg/cmd/roachtest/tests/registry.go

@@ -148,7 +148,6 @@ func RegisterTests(r registry.Registry) {
 	registerTypeORM(r)
 	registerUnoptimizedQueryOracle(r)
 	registerValidateSystemSchemaAfterVersionUpgrade(r)
-	registerVersion(r)
 	registerYCSB(r)
 	registerDeclarativeSchemaChangerJobCompatibilityInMixedVersion(r)
 }