doc/ja: remove old Japanese man page translations
They were added way back in 2005 and haven't been updated since. They
are no longer referenced by the Makefiles at upper levels and have not
been shipped with a recent version of Mercurial.
i18n-sv: synchronized with
f4f3a74ce832
i18n-pt_BR: synchronized with
b1339234080e
ui: ignore ui.logtemplate and ui.style when HGPLAIN is set
HGPLAIN should suppress them because they change Mercurial's default
output.
i18n-ja: synchronized with
bb4561401c84