For example:
sed 's/\u0091//g' file1
Right now, I have to do hexdump to get hex number and put into sed as follows:
$ echo -ne '\u9991' | hexdump -C
00000000 e9 a6 91 |...|
00000003
And then:
$ sed 's/\xe9\xa6\x91//g' file1