Twenty Nineteen: Search widget input field width is too narrow on wide screens

[crunnells]

At screens below ~600px, the search input field is 100% of the parent container, but above that it changes to width: auto; which causes it to shrink to ~170px. I suggest we make that a little larger by removing auto and setting a max-width in the CSS.

Below 598px:

Above 600px:

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This issue was migrated over from Twenty Nineteen's GitHub repository:

​https://github.com/WordPress/twentynineteen/issues/747

[achyuthajoy]

Removed media query to make the search widget input width to 100%

[achyuthajoy]

Haven't added a max-width parameter which would allow the user to add additional CSS without much overrides.