Remove magnifier icon in select2 search field

[ishikawa999]

Due to the impact of Propshaft support, there is an issue in RedMica 3.0 where the magnifying glass icon does not appear when the searchable select box feature is enabled. I have decided to remove the magnifying glass icon since it is still clear that the select box is searchable without it.

Additionally, for the Bleuclair theme, the magnifying glass icon and padding are added on the theme side, so the display remains unchanged.

selectbox before changes	selectbox after changes	selectbox after changes(with bleuclair theme)

[ishikawa999]

Thanks for reviewing. Merging.