Two formatted reports introduced in e239c7f43c used a type defined at
compile time using the PRId64 macro. Translation failed for these
messages, because the message was extracted as:
"No keyframes removed from % strip(s)"
and the type was lost at the time formatting happened.
This commit instead uses fmt to format the message, which deals with
using the proper int type depending on the platform.
Pull Request: https://projects.blender.org/blender/blender/pulls/144374