Fix modern metalint nits

Fix modern metalint nits

These are detected by metalint since SVN r132 /
 https://github.com/rmanfredi/dist/commit/8160f5523cbbb37197732ea645d02f884e180f3c

with
 "d_statfs3.U": unknown private file 'try.h'.
 "d_statfs4.U": unknown private file 'try.h'.
 "d_union_semun.U": unknown private file 'tryh.h'.
 "dtraceobject.U": unknown private file 'perldtrace.h'.

Even though $rm_try removes try.[cho] anyway, we clean try.h
explicitly to work around the resulting
 "U/perl/d_statfs4.U": unused temporary file 'try.h'.
warnings which seem like a bug in metalint.