build-wine: allow local testing

Before, it was only possible to test commits that are
on Github (pull request or merged). Now, changes can be
tested locally too.

This introduces the risk that a release could be built
containing uncommitted changes which by definition breaks
deterministic builds. Fortunately, this will always be
detected because the version string is created using
`git describe --tags --dirty`.

Also, retire $TARGET variable because it decouples the
build scripts from the commit revision to be built. This
is a problem for deterministic  builds.

contrib/build-wine/electrum.nsi

@@ -72,7 +72,7 @@
   !define MUI_ABORTWARNING
   !define MUI_ABORTWARNING_TEXT "Are you sure you wish to abort the installation of ${PRODUCT_NAME}?"
   
-  !define MUI_ICON "tmp\electrum\icons\electrum.ico"
+  !define MUI_ICON "c:\electrum\icons\electrum.ico"
   
 ;--------------------------------
 ;Pages
@@ -111,7 +111,7 @@ Section
   
   ;Files to pack into the installer
   File /r "dist\electrum\*.*"
-  File "..\..\icons\electrum.ico"
+  File "c:\electrum\icons\electrum.ico"
 
   ;Store installation folder
   WriteRegStr HKCU "Software\${PRODUCT_NAME}" "" $INSTDIR