remove workaround for controlling terminal behavior in repl_cmd

This was originally added as a workaround for the behavior of sh to try
to become the terminal process group leader, but no longer relevant
since #25006 removed that flag again:
```
julia> run(detach(`bash -i -c "sleep 0"`))
bash: cannot set terminal process group (-1): Inappropriate ioctl for device
bash: no job control in this shell
Process(`bash -i -c 'sleep 0'`, ProcessExited(0))
```

Julia recieves SIGTTOU when a process like "sh -i -c" exits (at least
for bash and zsh, but not dash, ksh, or csh), since "sh -i" sometimes
takes over the controlling terminal, causing julia to stop once the bash
process exits. This can be quite annoying, but julia goes through some
pains (in libuv) to ensure it doesn't steal the controlling terminal
from the parent, and apparently bash is not so careful about it.
However, since PR #25006, julia hasn't needed this workaround for this
issue, so we can now follow the intended behavior when the child is in
the same session group and steals the controlling terminal from the
parent. Even if such behavior seems odd, this seems to be the intended
behavior per posix design implementation that it gets SIGTTOU when julia
later tries to change mode (from cooked -> raw after printing the
prompt): http://curiousthing.org/sigttin-sigttou-deep-dive-linux.

```
$ ./julia -q
shell> bash -i -c "sleep 1"

[1]+  Stopped                 ./julia

julia> run(`zsh -i -c "sleep 0"`)
Process(`zsh -i -c 'sleep 0'`, ProcessExited(0))

julia>
[1]+  Stopped                 ./julia
```

Author: vtjnash

base/client.jl

@@ -32,9 +32,6 @@ stackframe_lineinfo_color() = repl_color("JULIA_STACKFRAME_LINEINFO_COLOR", :bol
 stackframe_function_color() = repl_color("JULIA_STACKFRAME_FUNCTION_COLOR", :bold)
 
 function repl_cmd(cmd, out)
-    shell = shell_split(get(ENV, "JULIA_SHELL", get(ENV, "SHELL", "/bin/sh")))
-    shell_name = Base.basename(shell[1])
-
     # Immediately expand all arguments, so that typing e.g. ~/bin/foo works.
     cmd.exec .= expanduser.(cmd.exec)
 
@@ -64,19 +61,15 @@ function repl_cmd(cmd, out)
         cd(dir)
         println(out, pwd())
     else
-        @static if !Sys.iswindows()
-            if shell_name == "fish"
-                shell_escape_cmd = "begin; $(shell_escape_posixly(cmd)); and true; end"
-            else
-                shell_escape_cmd = "($(shell_escape_posixly(cmd))) && true"
-            end
+        if !Sys.iswindows()
+            shell = shell_split(get(ENV, "JULIA_SHELL", get(ENV, "SHELL", "/bin/sh")))
+            shell_escape_cmd = shell_escape_posixly(cmd)
             cmd = `$shell -c $shell_escape_cmd`
         end
         try
             run(ignorestatus(cmd))
         catch
-            # Windows doesn't shell out right now (complex issue), so Julia tries to run the program itself
-            # Julia throws an exception if it can't find the program, but the stack trace isn't useful
+            # Julia throws an exception if it can't find the cmd (which may be the shell itself), but the stack trace isn't useful
             lasterr = current_exceptions()
             lasterr = ExceptionStack([(exception = e[1], backtrace = [] ) for e in lasterr])
             invokelatest(display_error, lasterr)