Remove obsolete AC_HEADER_TIME to fix configure warning on Linux

[sendaoYan]

Summary

• Remove the obsolete AC_HEADER_TIME macro from configure.ac.
• Fixes the shell warning during ./configure on non-Solaris hosts:
  ./configure: line 4816: test: =: unary operator expected

Problem

AC_HEADER_TIME is obsolete in Autoconf 2.71. The generated configure script contains legacy shell code:

if test $ac_cv_header_sys_time_h = yes; then

On Linux, ac_cv_header_sys_time_h is never set because the header check loop that populates it only runs inside the solaris*) branch. The empty variable expands to test = yes, which triggers the unary-operator error.

Configure still completes, but the warning is confusing and indicates broken autotools usage.

issue: #22

Solution

Drop AC_HEADER_TIME entirely. The project does not rely on TIME_WITH_SYS_TIME (it is obsolete); corkscrew.c includes <sys/time.h> directly.