Remove trailing blanks
Remove trailing blanks

Remove trailing blanks.  They can cause mysterious merge problems
later (because lines that "look" the same aren't), as well as causing
text editor motions to be odd (because the "end" of the line isn't the end).

Signed-off-by: David A. Wheeler <9ae72d22d8b894b865a7a496af4fab6320e6abb2@dwheeler.com>

metamath/set.mm,metamath/set.mm,metamath/set.mm