Partially fix "make check"

Remove the code that was used for determining the OS, because newer
rubies warn the usage of deprecated Config. The information of the OS is
actually not used anywhere.

Fix the result for examples.rb:Sec_3_44_2. Now #write "%e" doesn't
output an extra blank line. (It was changed by 44cf65fbe0.)

NOTE: For automake >= 1.13, "serial-tests" option has to be added in
AM_INIT_AUTOMAKE in configure.ac:

  AM_INIT_AUTOMAKE([foreign 1.7 dist-bzip2 serial-tests])

otherwise "make check" causes errors (#13), while adding "serial-tests"
causes an error at running automake < 1.12.