Remove dead BitcoinUnits::id code and update assets-attribution for non-image unit selector

doc/assets-attribution.md

@@ -39,9 +39,7 @@ Jonas Schnelli
     src/qt/res/icons/connect[0-3].png, src/qt/res/icons/eye_minus.png,
     src/qt/res/icons/eye_plus.png, src/qt/res/icons/verify.png,
     src/qt/res/icons/tx_inout.png, src/qt/res/icons/tx_input.png,
-    src/qt/res/icons/unit_btc.png, src/qt/res/icons/unit_mbtc.png,
-    src/qt/res/icons/unit_ubtc.png, src/qt/res/src/verify.svg
-    src/qt/res/src/bitcoin.svg, src/qt/res/src/clock*.svg,
-    src/qt/res/src/connect*.svg, src/qt/res/src/mine.svg,
-    src/qt/res/src/qt.svg, src/qt/res/src/tx*.svg,
+    src/qt/res/src/verify.svg, src/qt/res/src/bitcoin.svg,
+    src/qt/res/src/clock*.svg, src/qt/res/src/connect*.svg,
+    src/qt/res/src/mine.svg, src/qt/res/src/qt.svg, src/qt/res/src/tx*.svg,
     src/qt/res/src/verify.svg,

src/qt/bitcoinunits.cpp

@@ -36,17 +36,6 @@ bool BitcoinUnits::valid(int unit)
     }
 }
 
-QString BitcoinUnits::id(int unit)
-{
-    switch(unit)
-    {
-    case BTC: return QString("btc");
-    case mBTC: return QString("mbtc");
-    case uBTC: return QString("ubtc");
-    default: return QString("???");
-    }
-}
-
 QString BitcoinUnits::name(int unit)
 {
     switch(unit)

src/qt/bitcoinunits.h

@@ -76,8 +76,6 @@ public:
     static QList<Unit> availableUnits();
     //! Is unit ID valid?
     static bool valid(int unit);
-    //! Identifier, e.g. for image names
-    static QString id(int unit);
     //! Short name
     static QString name(int unit);
     //! Longer description