Reenable bwc tests (#43872)

This reenables the BWC tests disabled in #43856

Author: tlrx

build.gradle

@@ -160,8 +160,8 @@ task verifyVersions {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
-final String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/43823" /* place a PR link here when committing bwc changes */
+boolean bwc_tests_enabled = true
+final String bwc_tests_disabled_issue = "" /* place a PR link here when committing bwc changes */
 if (bwc_tests_enabled == false) {
   if (bwc_tests_disabled_issue.isEmpty()) {
     throw new GradleException("bwc_tests_disabled_issue must be set when bwc_tests_enabled == false")

rest-api-spec/src/main/resources/rest-api-spec/test/indices.stats/20_translog.yml

@@ -81,8 +81,8 @@ setup:
 ---
 "Translog stats on closed indices":
   - skip:
-      version: " - 7.9.99"
-      reason:  "closed indices have translog stats starting version 8.0.0"
+      version: " - 7.2.99"
+      reason:  "closed indices have translog stats starting version 7.3.0"
 
   - do:
       index:
@@ -111,6 +111,7 @@ setup:
   - do:
       indices.close:
         index: test
+        wait_for_active_shards: 1
   - is_true: acknowledged
 
   - do:

x-pack/plugin/src/test/resources/rest-api-spec/test/indices.freeze/20_stats.yml

@@ -10,8 +10,8 @@ setup:
 ---
 "Translog stats on frozen indices":
   - skip:
-      version: " - 7.9.99"
-      reason:  "frozen indices have translog stats starting version 8.0.0"
+      version: " - 7.2.99"
+      reason:  "frozen indices have translog stats starting version 7.3.0"
 
   - do:
       index: