Revert "Add libc::c_bool type."

This reverts commit c700e64.

Author: jimblandy

libc-test/build.rs

@@ -36,7 +36,6 @@ fn main() {
     cfg.header("errno.h")
        .header("fcntl.h")
        .header("limits.h")
-       .header("stdbool.h")
        .header("stddef.h")
        .header("stdint.h")
        .header("stdio.h")

src/lib.rs

@@ -109,7 +109,6 @@ pub type uint16_t = u16;
 pub type uint32_t = u32;
 pub type uint64_t = u64;
 
-pub type c_bool = u8;
 pub type c_schar = i8;
 pub type c_uchar = u8;
 pub type c_short = i16;