misc: Revert v21.2 specific commits for develop

These changes were made to the release staging branch for the v21.2
release. This commit reverts them for the develop branch.

Change-Id: I9f02470d00d5034a0797f32d4c1fe0e7055860a6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54904
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/Doxyfile

@@ -31,7 +31,7 @@ PROJECT_NAME           = gem5
 # This could be handy for archiving the generated documentation or 
 # if some version control system is used.
 
-PROJECT_NUMBER         = v21.2.0.0
+PROJECT_NUMBER         = DEVELOP-FOR-V22-0
 
 # The OUTPUT_DIRECTORY tag is used to specify the (relative or absolute) 
 # base path where the generated documentation will be put. 

src/base/version.cc

@@ -32,6 +32,6 @@ namespace gem5
 /**
  * @ingroup api_base_utils
  */
-const char *gem5Version = "21.2.0.0";
+const char *gem5Version = "[DEVELOP-FOR-v22.0";
 
 } // namespace gem5

src/python/gem5/resources/downloader.py

@@ -45,7 +45,7 @@ def _resources_json_version_required() -> str:
     """
     Specifies the version of resources.json to obtain.
     """
-    return "21.2"
+    return "develop"
 
 def _get_resources_json_uri() -> str:
     uri = (