de-lint code base: remove unused variables

* unused variables removed via comment or replacement with $null

* NOTE: using PSScriptAnalyzer as the lint analyzer

lib/core.ps1

@@ -1,6 +1,6 @@
 $scoopdir = $env:SCOOP, "~\appdata\local\scoop" | select-object -first 1
 $globaldir = $env:SCOOP_GLOBAL, "$($env:programdata.tolower())\scoop" | select-object -first 1
-$cachedir = "$scoopdir\cache" # always local
+#$cachedir = "$scoopdir\cache" # always local
 
 $CMDenvpipe = $env:SCOOP__CMDenvpipe
 
@@ -135,10 +135,10 @@ function shim($path, $global, $name, $arg) {
 
     $shim = "$abs_shimdir\$($name.tolower()).ps1"
 
-    # convert to relative path
-    push-location $abs_shimdir
-    $relative_path = resolve-path -relative $path
-    pop-location
+    # # convert to relative path
+    # push-location $abs_shimdir
+    # $relative_path = resolve-path -relative $path
+    # pop-location
 
     write-output '# ensure $HOME is set for MSYS programs' | out-file $shim -encoding oem
     write-output "if(!`$env:home) { `$env:home = `"`$home\`" }" | out-file $shim -encoding oem -append

lib/decompress.ps1

@@ -11,7 +11,7 @@ function file_requires_7zip($fname) {
 }
 
 function extract_7zip($path, $to, $recurse) {
-    $output = 7z x "$path" -o"$to" -y
+    $null = 7z x "$path" -o"$to" -y
     if($lastexitcode -ne 0) { abort "exit code was $lastexitcode" }
 
     # check for tar

lib/install.ps1

@@ -419,7 +419,7 @@ function msi_installed($code) {
     $name = $key.getvalue('displayname')
     $version = $key.getvalue('displayversion')
     $classkey = "IdentifyingNumber=`"$code`",Name=`"$name`",Version=`"$version`""
-    try { $wmi = [wmi]"Win32_Product.$classkey"; $true } catch { $false }
+    try { $null = [wmi]"Win32_Product.$classkey"; $true } catch { $false }
 }
 
 function install_prog($fname, $dir, $installer) {