Remove superfluous preprocessor tests from some cmd_*.c files.

A small number of common/cmd_*.c files contain preprocessor tests that
are apparently superfluous since those same tests are used in the
Makefile to control the compilation of those files.  Those tests are
clearly redundant as long as they surround the entirety of the source
in those files.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>