configure.ac: remove unnecessary checks
configure.ac: remove unnecessary checks

Remove all unused program, header, and function checks to speed up the
configure script.

With some exceptions, the AC_PROG_*, AC_CHECK_HEADERS, and
AC_CHECK_FUNCS macros in configure.ac were not doing much.  If a
program, header, or function was missing, the configure script
continued without error and no alternative behavior was selected
(e.g., enable a replacement function or disable an optional feature).

Rather than test every possible utility, header, or function that
might be used, a better approach is to:

  * Assume the platform follows a standard or standards (e.g., C99,
    POSIX Issue 7, 2013 edition).
  * Where convenient, test to see if the platform at least appears to
    conform to the standard(s) (e.g., AC_PROG_CC_C99).
  * Don't bother testing for specific standard behavior unless the
    software fails to build or function properly on a platform of
    interest (due to lack of standard conformance).
  * Add autoconf tests for any behavior not completely specified by
    the standard(s) (e.g., MySQL).

Note that this removes some MySQL header and function tests.  The
removed tests are not necessary because there are already adequate
MySQL tests (involving the mysql_config utility).

rhansen/rpstir,rhansen/rpstir,rhansen/rpstir,rhansen/rpstir,rhansen/rpstir