test: drop whitespace after shell redirection operators

(The one case that is left unchanged is '< <(subcommand)'.)

This way, the style with no gap was already dominant. This way, the reader
immediately knows that ' < ' is a comparison operator and ' << ' is a shift.

In a few cases, replace custom EOF replacement by just EOF. There is no point
in using someting like "_EOL" unless "EOF" appears in the text.

docs/HACKING.md

@@ -206,7 +206,7 @@ achieve this, create a script with the following contents in systemd's project d
 
 ```sh
 #!/usr/bin/env sh
-tee mkosi-clangd.build > /dev/null << EOF
+tee mkosi-clangd.build >/dev/null <<EOF
 #!/usr/bin/env sh
 exec clangd \\
         --compile-commands-dir=/root/build \\