Don't use awk for eaw table generation. Remove code gen'd file too.

Summary:

The update to `libmbfl` exposed a problem when using `awk` to generate
`libmbfl/mbfl/eaw_table.h` where `strtonum` was not being found. So, let's
not rely on `awk`, but instead just rely on `gawk`. Also remove the auto
generated `eaw_table.h` from the repo as well.

Fixes: https://github.com/hhvm/packaging/issues/88