Don't modify the kill-ring in elm-sort-imports

[appleby]

Use delete-region instead of kill-region in elm-sort-imports.

Consider the following sequence of commands:

1. kill some text in buffer A
2. save buffer A
3. switch to buffer B
4. yank text from kill-ring

Prior to this change, if a user had enabled elm-sort-imports-on-save, then when yanking text in step 4, they would not get the text killed in step 1, but rather the import list killed by elm-sort-imports.

[baransu]

Found this issue recently. Glad someone fixed it. Waiting for merge :D

[jasonm23]

:+1: