An in-app update restart inherits the old mount's entries alongside the
new one's: the restarted IDE's LD_LIBRARY_PATH holds both mounts, and
children (host curl downloading a language server) still load the old
image's bundled libraries.
appimage_env_fixes now drops ':'-separated entries under any
/tmp/.mount_* path, not just the current $APPDIR's: an entry under a
different mount is another image's, never the host's.
Fixes#1966
arookieofc
c614355753