ci: remove obsoleted if/when-let and shadowed dynamic variable and fix some byte-compile warnings

[kiennq]

This fixes:

• obsoleted if/when-let form
• shadowed dynamic variables in lsp-protocol (standard-output to be exact)
• And some byte-compile warnings

There're still quite a few byte-compile warnings left, but I would like to invite anyone who has spare cycles to chimp in to fix them together

[jcs090218]

Do you know why if-let and when-let is deprecated? I hope they don't since I have used those macros in many places. 😅

[kiennq]

Do you know why if-let and when-let is deprecated? I hope they don't since I have used those macros in many places. 😅

They switched to if/when-let* form

+++
** 'if-let' and 'when-let' are now obsolete.
Use 'if-let*', 'when-let*' and 'and-let*' instead.

This effectively obsoletes the old '(if-let (SYMBOL SOMETHING) ...)'
single binding syntax, which we'd kept only for backwards compatibility.