Revert updates to Ubuntu 21.04 and pin to previous serial

Due to bug https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1916485 we are
 holding back any updates to the Ubuntu 21.04 images until resolved.

library/ubuntu

@@ -38,10 +38,16 @@ Tags: 20.10, groovy-20210225, groovy, rolling
 Architectures: amd64, arm32v7, arm64v8, ppc64le, s390x
 Directory: groovy
 
-# 20210224 (hirsute)
-Tags: 21.04, hirsute-20210224, hirsute, devel
+# 20210119 (hirsute)
+Tags: 21.04, hirsute-20210119, hirsute, devel
 Architectures: amd64, arm32v7, arm64v8, ppc64le, s390x
 Directory: hirsute
+amd64-GitCommit: ec931883d8292935b62ac40757287491e6ff467e
+arm32v7-GitCommit: f2ed9c714e4231e0d964095eaba5504fb4ce017d
+arm64v8-GitCommit: 69b377c4bbe13073c3ae2dd0c541dc7b52cc32ba
+i386-GitCommit: 68ae4b1742136f031c3a4770e3e4776a3618df1f
+ppc64le-GitCommit: eb34d4327f126b9f60a873362854b09293f6d9ff
+s390x-GitCommit: 0342e501a11386aedd5597555481cb9b10921eda
 
 # 20191217 (trusty)
 Tags: 14.04, trusty-20191217, trusty