If you do hg log myfile -v you see a list of changesets that the file was modified in.
In our case, in the most recent changeset, the file was removed. But
You can check which revision deleted a file (any many other interesting features) using revsets:
hg log -r 'removes(
Some examples:
hg log -r 'removes(build.xml)' // where build.xml used to be in the current directory
hg log -r 'removes("**/build.xml")' // where build.xml may have been in sub directories
See hg help revsets for details.