remove old deprecated commands (#9840)

# Description
in this PR i propose to remove the following old deprecated commands
- `hash base64` -> `encode base64`
- `math eval` -> `math <sub>`
- `str to-datetime` -> `into datetime`
- `str to-decimal` -> `into decimal`
- `str find-replace` -> `str replace`
- `str to-int` -> `into int`
- `keep` -> `take`
- `match` -> `find`
- `nth` -> `select`
- `pivot` -> `transpose`
- `unalias` -> `hide`
- `all?` -> `all`
- `any?` -> `any`
- `empty?` -> `is-empty`
- `build-string` -> `str join` / string concatenation with `+`
- `str lpad` -> `fill`
- `str rpad` -> `fill`
- `str collect` -> `str join`
- `old-alias` -> `alias`

so old i do not remember them at all 😮

i left the following four commands because they have been moved much
more recently i think!
- `fetch` -> `http get`
- `post` -> `http post`
- `benchmark` -> `timeit`
- `let-env`
- `date format` -> `format date`

# User-Facing Changes

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- ⚫ `toolkit test`
- ⚫ `toolkit test stdlib`

# After Submitting

crates/nu-command/src/default_context.rs

@@ -299,8 +299,6 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
 
         // Env
         bind_command! {
-            LetEnvDeprecated,
-            DateFormat,
             ExportEnv,
             LoadEnv,
             SourceEnv,
@@ -382,15 +380,8 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
 
         // Deprecated
         bind_command! {
-            HashBase64,
-            LPadDeprecated,
-            MathEvalDeprecated,
-            RPadDeprecated,
-            StrCollectDeprecated,
-            StrDatetimeDeprecated,
-            StrDecimalDeprecated,
-            StrFindReplaceDeprecated,
-            StrIntDeprecated,
+            LetEnv,
+            DateFormat,
         };
 
         working_set.render()