Remove unneeded encode/decode methods.

In rust-lang#110927 the encode/decode methods for `i8`, `char`, `bool`, and `str`
were made inherent. This commit removes some unnecessary implementations
of these methods that were missed in that PR.

Author: nnethercote

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -108,11 +108,7 @@ impl<'a, 'tcx> Encoder for EncodeContext<'a, 'tcx> {
         emit_i64(i64);
         emit_i32(i32);
         emit_i16(i16);
-        emit_i8(i8);
 
-        emit_bool(bool);
-        emit_char(char);
-        emit_str(&str);
         emit_raw_bytes(&[u8]);
     }
 }

compiler/rustc_middle/src/query/on_disk_cache.rs

@@ -1026,11 +1026,7 @@ impl<'a, 'tcx> Encoder for CacheEncoder<'a, 'tcx> {
         emit_i64(i64);
         emit_i32(i32);
         emit_i16(i16);
-        emit_i8(i8);
 
-        emit_bool(bool);
-        emit_char(char);
-        emit_str(&str);
         emit_raw_bytes(&[u8]);
     }
 }

compiler/rustc_middle/src/ty/codec.rs

@@ -518,11 +518,6 @@ macro_rules! implement_ty_decoder {
                     read_i64 -> i64;
                     read_i32 -> i32;
                     read_i16 -> i16;
-                    read_i8 -> i8;
-
-                    read_bool -> bool;
-                    read_char -> char;
-                    read_str -> &str;
                 }
 
                 #[inline]