Remove gdb.base/coremaker2.c

Remove gdb.base/coremaker2.c

I happen to find that coremaker2.c isn't used in the testsuite (if I
don't miss anything).  I don't believe it until I see this ChangeLog
entry,

1999-11-18  Fred Fish  <fnf@cygnus.com>

        * gdb.base/coremaker2.c: Add sample program for generating
        cores that is more self contained than coremaker.c.  Eventually
        I'll add more code to this and tie it into the testsuite.

looks Fred didn't "tie it into testsuite" later.

gdb/testsuite:

2015-12-11  Yao Qi  <yao.qi@linaro.org>

	* gdb.base/coremaker2.c: Remove.