INSTALL: Updated MSVC 6 caveats

To use an up to date download link as well as remove duplicate
information.

docs/INSTALL

@@ -252,8 +252,10 @@ Win32
    MSVC 6 caveats
    --------------
 
-   If you use MSVC 6 it is required that you use the February 2003 edition PSDK:
-   http://www.microsoft.com/msdownload/platformsdk/sdkupdate/psdk-full.htm
+   If you use MSVC 6 it is required that you use the February 2003 edition of
+   the 'Platform SDK' which can be downloaded from:
+
+   http://www.microsoft.com/en-us/download/details.aspx?id=12261
 
    Building any software with MSVC 6 without having PSDK installed is just
    asking for trouble down the road once you have released it, you might notice
@@ -261,8 +263,6 @@ Win32
    choice of static vs dynamic runtime and third party libraries. Anyone using
    software built in such way will at some point regret having done so.
 
-   When someone uses MSVC 6 without PSDK he is using a compiler back from 1998.
-
    If the compiler has been updated with the installation of a service pack as
    those mentioned in http://support.microsoft.com/kb/194022 the compiler can be
    safely used to read source code, translate and make it object code.
@@ -272,13 +272,6 @@ Win32
    header files and libraries with bugs and security issues which have already
    been addressed and fixed long time ago.
 
-   In order to make use of the updated system headers and fixed libraries
-   for MSVC 6, it is required that 'Platform SDK', PSDK from now onwards,
-   is installed. The specific PSDK that must be installed for MSVC 6 is the
-   February 2003 edition, which is the latest one supporting the MSVC 6 compiler,
-   this PSDK is also known as 'Windows Server 2003 PSDK' and can be downloaded
-   from http://www.microsoft.com/msdownload/platformsdk/sdkupdate/psdk-full.htm
-
    So, building curl and libcurl with MSVC 6 without PSDK is absolutely
    discouraged for the benefit of anyone using software built in such
    environment. And it will not be supported in any way, as we could just