Drop implicit minimum sizing from PC2 and PC3 Buttons

For the following reasons:
- It can break and look bad on Plasma Mobile which uses the Plasma style
- It makes buttons with icons and short text look visually unbalanced
- QStyle and QML desktop style buttons do not do this so it's a source
  of inconsistency

Tests are adjusted to all pass. Stuff looks better to my eye.

src/declarativeimports/plasmacomponents3/Button.qml

@@ -27,7 +27,7 @@ import "private" as Private
 T.Button {
     id: control
 
-    implicitWidth: Math.max( (label.visible ? units.gridUnit * 6 : units.gridUnit), contentItem.implicitWidth)
+    implicitWidth: Math.max(units.gridUnit, contentItem.implicitWidth)
                             + leftPadding + rightPadding
     implicitHeight: Math.max(units.gridUnit, contentItem.implicitHeight)
                             + topPadding + bottomPadding

src/declarativeimports/plasmastyle/ButtonStyle.qml

@@ -113,17 +113,6 @@ QtQuickControlStyle.ButtonStyle {
     }
 
     background: Item {
-
-        implicitHeight: Math.floor(Math.max(theme.mSize(theme.defaultFont).height*1.6, style.minimumHeight))
-
-        implicitWidth: {
-            if (control.text.length == 0) {
-                height;
-            } else {
-                theme.mSize(theme.defaultFont).width*12
-            }
-        }
-
         opacity: enabled ? 1.0 : 0.5
 
         Private.ButtonShadow {

tests/components/button.qml

@@ -29,7 +29,7 @@ ComponentBase {
         }
 
         Label {
-            text: "text alone, should be about 12 chars wide"
+            text: "text alone, should be about as wide as the text itself"
         }
 
         PlasmaComponents.Button {

tests/components/button3.qml

@@ -28,7 +28,7 @@ ComponentBase {
         }
 
         PlasmaComponents.Label {
-            text: "text alone, should be about 12 chars wide"
+            text: "text alone, should be about as wide as the text itself"
         }
 
         PlasmaComponents.Button {