qbs: Remove pointless ExtensionSystem dependency from plugins

A QtcPlugin depends on ExtensionSystem, so there is no need to restate
the dependency.

Change-Id: I8e0cb5f94858e912f5ce528ee67b683d4d837c27
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/clangformat/clangformat.qbs

@@ -1,5 +1,4 @@
 import qbs
-import qbs.FileInfo
 
 QtcPlugin {
     name: "ClangFormat"
@@ -8,7 +7,6 @@ QtcPlugin {
     Depends { name: "TextEditor" }
     Depends { name: "CppTools" }
     Depends { name: "ProjectExplorer" }
-    Depends { name: "ExtensionSystem" }
     Depends { name: "Utils" }
 
     Depends { name: "libclang"; required: false }

src/plugins/clangtools/clangtools.qbs

@@ -8,7 +8,6 @@ QtcPlugin {
     Depends { name: "Core" }
     Depends { name: "TextEditor" }
     Depends { name: "CppTools" }
-    Depends { name: "ExtensionSystem" }
     Depends { name: "ProjectExplorer" }
     Depends { name: "QtcSsh" }
     Depends { name: "Utils" }

src/plugins/cppcheck/cppcheck.qbs

@@ -5,7 +5,6 @@ QtcPlugin {
 
     Depends { name: "Core" }
     Depends { name: "CppTools" }
-    Depends { name: "ExtensionSystem" }
     Depends { name: "ProjectExplorer" }
     Depends { name: "TextEditor" }
     Depends { name: "Utils" }