add a compose sequence with double dead_tilde for `≈` (almost_equal_to)

Inputting two dead tildes in a row or dead tilde + space without compose key already results in asciitilde. Having this behavior replicated in compose key is redundant. Two dead tildes with compose key used to result in almost equal to sign so I reversed the behavior. I do not know where the line should be placed so feel free move it if you know a better place for this.