Installer: Make SetEnvironmentVariable also available during uninstall

This fixes the "Runtime Error (at 18:1292): Could not call proc." as
reported by Pau Garcia i Quiles <pgquiles@elpauer.org> on the mailing
list.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>

share/WinGit/helpers.inc.iss

@@ -91,9 +91,9 @@ end;
 // Sets the contents of the specified environment variable for the current process.
 function SetEnvironmentVariable(lpName,lpValue:String):Boolean;
 #ifdef UNICODE
-external 'SetEnvironmentVariableW@Kernel32.dll stdcall delayload setuponly';
+external 'SetEnvironmentVariableW@Kernel32.dll stdcall delayload';
 #else
-external 'SetEnvironmentVariableA@Kernel32.dll stdcall delayload setuponly';
+external 'SetEnvironmentVariableA@Kernel32.dll stdcall delayload';
 #endif
 
 // Sets the environment variable "VarName" to the concatenation of "DirStrings"