Update dartdoc to 0.42.0.

Also removes the mustache dependency from the SDK.

Release notes: https://github.com/dart-lang/dartdoc/releases/tag/v0.42.0

Change-Id: I2c97e1be180199db3a520f3fa020973761781dbf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/194011
Reviewed-by: Devon Carew <devoncarew@google.com>
Commit-Queue: Janice Collins <jcollins@google.com>

.dart_tool/package_config.json

@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2021-03-29T21:48:35.411283",
+  "generated": "2021-04-05T08:58:24.237896",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -442,12 +442,6 @@
       "packageUri": "lib/",
       "languageVersion": "2.2"
     },
-    {
-      "name": "mustache",
-      "rootUri": "../third_party/pkg/mustache",
-      "packageUri": "lib/",
-      "languageVersion": "2.0"
-    },
     {
       "name": "native_stack_traces",
       "rootUri": "../pkg/native_stack_traces",

DEPS

@@ -102,7 +102,7 @@ vars = {
 
   "chromedriver_tag": "83.0.4103.39",
   "browser_launcher_rev": "12ab9f351a44ac803de9bc17bb2180bb312a9dd7",
-  "dartdoc_rev" : "e2d010ed74059be942a78ced5f35f1b8d667ed16",
+  "dartdoc_rev" : "505f163f7cb48e917503e4a23fbff1227e08b263",
   "ffi_rev": "f3346299c55669cc0db48afae85b8110088bf8da",
   "fixnum_rev": "16d3890c6dc82ca629659da1934e412292508bba",
   "file_rev": "0e09370f581ab6388d46fda4cdab66638c0171a1",
@@ -126,7 +126,6 @@ vars = {
   "matcher_rev": "1f7b6f0cb15eb6659a1de0513571575a5c8a51d0",
   "mime_rev": "c931f4bed87221beaece356494b43731445ce7b8",
   "mockito_rev": "d39ac507483b9891165e422ec98d9fb480037c8b",
-  "mustache_rev": "664737ecad027e6b96d0d1e627257efa0e46fcb1",
   "oauth2_rev": "7cd3284049fe5badbec9f2bea2afc41d14c01057",
   "package_config_rev": "a84c0d45401f215fbe9384df923a38f4022a3c45",
   "path_rev": "407ab76187fade41c31e39c745b39661b710106c",
@@ -379,10 +378,6 @@ deps = {
       Var("dart_git") + "mime.git" + "@" + Var("mime_rev"),
   Var("dart_root") + "/third_party/pkg/mockito":
       Var("dart_git") + "mockito.git" + "@" + Var("mockito_rev"),
-  Var("dart_root") + "/third_party/pkg/mustache":
-      Var("dart_git")
-      + "external/github.com/xxgreg/mustache"
-      + "@" + Var("mustache_rev"),
   Var("dart_root") + "/third_party/pkg/oauth2":
       Var("dart_git") + "oauth2.git" + "@" + Var("oauth2_rev"),
   Var("dart_root") + "/third_party/pkg_tested/package_config":