Revert "Workaround: build for Varnish >=5.2.0, when _Static_assert is defined."

This reverts commit 35e21c5f.

No longer needed since the fix for Varnish issue 2449.

configure.ac

@@ -130,24 +130,6 @@ if test "x$enable_debugging" != "xno"; then
 	AC_LANG_POP()
 fi
 
-# Varnish since 5.2.0 depends on AC_DEFINE(STATIC_ASSERT)
-save_LIBS="${LIBS}"
-LIBS=""
-AC_CACHE_CHECK([for _Static_assert],
-  [ac_cv_static_assert],
-  [AC_RUN_IFELSE(
-    [AC_LANG_PROGRAM([[
-_Static_assert(1 == sizeof(char), "didn't work");
-    ]],[[
-    ]])],
-    [ac_cv_static_assert=yes],
-    [ac_cv_static_assert=no])
-  ])
-if test "$ac_cv_static_assert" = yes; then
-   AC_DEFINE([STATIC_ASSERT], [1], [Define if _Static_assert is availabel])
-fi
-LIBS="${save_LIBS}"
-
 AC_CONFIG_FILES([
 	Makefile
 	src/Makefile