Do not use qmake and cmake generator automatically for each conanfile

Keep conanfiles self-contained. "txt" generator is not going to be used
by coin internally, drop it.

Task-number: QTQAINFRA-998
Change-Id: I80ffb7342e07d8ef883bed6de77ac9646479f145
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

coin/provisioning/common/conan.ps1

@@ -23,7 +23,7 @@ function Run-Conan-Install
         Start-Process `
             "C:\Utils\Conan\conan\conan.exe" `
             -WorkingDirectory $outpwd `
-            -ArgumentList "install -i -f $($_.FullName) -g txt -g qmake -g cmake", `
+            -ArgumentList "install -i -f $($_.FullName)", `
                 '-s', ('compiler="' + $Compiler + '"'), `
                 "-s os=Windows -s arch=$($Arch) -s compiler.version=$($CompilerVersion)" `
             -NoNewWindow -Wait

coin/provisioning/qtci-windows-10-x86/conanfiles/qtwebkit.txt

@@ -5,6 +5,7 @@ libxml2-qt/2.9.4@Vitallium/stable
 libxslt-qt/1.1.29@Vitallium/stable
 
 [generators]
+cmake
 virtualenv
 
 [options]

coin/provisioning/qtci-windows-10-x86_64/conanfiles/qtwebkit.txt

@@ -5,6 +5,7 @@ libxml2-qt/2.9.4@Vitallium/stable
 libxslt-qt/1.1.29@Vitallium/stable
 
 [generators]
+cmake
 virtualenv
 
 [options]