Remove index.mapper.dynamic from watcher and security templates

index.mapper.dynamic should not be used for 6.0+ indices, so this commit removes it from the
templates used by security and watcher.

Relates elastic/elasticsearch#25734

Original commit: elastic/x-pack-elasticsearch@766eebe660

plugin/src/main/resources/security_audit_log.json

@@ -2,8 +2,7 @@
   "index_patterns": ".security_audit_log*",
   "order": 2147483647,
   "settings": {
-    "index.format": 6,
-    "index.mapper.dynamic" : false
+    "index.format": 6
   },
   "mappings": {
     "doc": {

plugin/src/main/resources/triggered-watches.json

@@ -3,7 +3,6 @@
   "order": 2147483647,
   "settings": {
     "index.number_of_shards": 1,
-    "index.mapper.dynamic" : false,
     "index.refresh_interval" : "-1",
     "index.format": 6,
     "index.priority": 900

plugin/src/main/resources/watch-history.json

@@ -4,8 +4,7 @@
   "settings": {
     "xpack.watcher.template.version": "${xpack.watcher.template.version}",
     "index.number_of_shards": 1,
-    "index.format": 6,
-    "index.mapper.dynamic": false
+    "index.format": 6
   },
   "mappings": {
     "doc": {

plugin/src/main/resources/watches.json

@@ -3,7 +3,6 @@
   "order": 2147483647,
   "settings": {
     "index.number_of_shards": 1,
-    "index.mapper.dynamic" : false,
     "index.format": 6,
     "index.priority": 800
   },