Revert "update release date"

This reverts commit e7ad68f8a97edccda81755be23f2345c44edb09a.
Revert "appcast for 1.5.4"

This reverts commit e7a1647235130be1213fe6b3d5880b466d8422e6.
Revert "Update release notes"

This reverts commit 1e85c2db8635212617a266d90a4303ddd4c1d5c4.
Revert "Update for CotEditor 1.5.4"

This reverts commit 3935b5c8e7001c62322c9fd3c16fbe77631fbfca.