Remove vestigial reference to /VAXC qualifier

This refers to building using DEC C but with a VAX C compatibility
mode.  Building Perl like that has not been supported for a long
time and it's not worth revisiting as that basically puts the
compiler into a K & R, pre-ANSI mode.

Author: craigberry

configure.com

@@ -1304,8 +1304,6 @@ $ WRITE CONFIG "#include <stdio.h>"
 $ WRITE CONFIG "int main() {"
 $ WRITE CONFIG "#ifdef __DECC"
 $ WRITE CONFIG "        printf(""/DECC\n"");"
-$ WRITE CONFIG "#else"
-$ WRITE CONFIG "        printf(""/VAXC\n"");"
 $ WRITE CONFIG "#endif"
 $ WRITE CONFIG "        exit(0);"
 $ WRITE CONFIG "}"