vim: Remove default setting of expandtab

An update from vim-cmake-syntax by commit v3.9.0-rc1~167^2^2
(vim-cmake-syntax 2017-05-02, 2017-05-02) brought in a change to set
`expandtab` in CMake language files.  This should be a per-project or
per-user choice instead, so drop the setting.

Auxiliary/vim/indent/cmake.vim

@@ -14,7 +14,6 @@ if exists("b:did_indent")
 endif
 let b:did_indent = 1
 
-setlocal et
 setlocal indentexpr=CMakeGetIndent(v:lnum)
 setlocal indentkeys+==ENDIF(,ENDFOREACH(,ENDMACRO(,ELSE(,ELSEIF(,ENDWHILE(