Revert "Utils: Allow (encoded) colons in host parts of FilePath"

This reverts commit f65b343c8a.

It's not needed anymore for the problem it was supposed to help with
(bad docker imange/qmake paths written by sdktool) and complicates
reasoning in this area.

Change-Id: Idef2ef9147d73e83461589907aa68c09721755cb
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/utils/filepath.cpp

@@ -213,13 +213,12 @@ QString FilePath::encodedHost() const
     QString result = host().toString();
     result.replace('%', "%25");
     result.replace('/', "%2f");
-    result.replace(':', "%3a");
     return result;
 }
 
 QString decodeHost(QString host)
 {
-    return host.replace("%25", "%").replace("%2f", "/").replace("%3a", ":");
+    return host.replace("%25", "%").replace("%2f", "/");
 }
 
 /*!