Remove $moduleclass_sfx from <input> and <button> elements

Removing the module class suffix from <input> and <button> elements in mod_search.

They're not needed for anything but it may well break layouts if a suffix is entered.
Also it's the only core module (I think) where it's applied to those elements. Normally it's only applied to the parent <div> where it makes sense as there is a specific module class.

This PR is based on a discussion in the JBS Google Group: 
https://groups.google.com/d/msg/joomlabugsquad/xCS5Npayc1M/h7G7FeiKo3UJ

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