fix: remove duplicate error handler from alpine-install.func (#11971)

- Remove legacy error_handler(), on_exit(), on_interrupt(), on_terminate() and set/trap definitions from alpine-install.func (already provided by error_handler.func which is sourced on line 10)

- The local error_handler() expected positional args as required, but catch_errors() sets trap as 'error_handler' (without args), causing unbound variable error with set -u (nounset)

- error_handler.func uses default values which is set -u safe

- Also align legacy trap in install.func network_check() to standard format

Fixes #11929

misc/install.func

@@ -172,7 +172,7 @@ network_check() {
   fi
 
   set -e
-  trap 'error_handler $LINENO "$BASH_COMMAND"' ERR
+  trap 'error_handler' ERR
 }
 
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