wallet: Remove ISMINE_WATCH_ONLY

ISMINE_WATCH_ONLY has been removed from all places it was being used,
and migration does not need ISMINE_WATCH_ONLY, so remove the enum.

src/wallet/scriptpubkeyman.cpp

@@ -204,7 +204,6 @@ isminetype LegacyDataSPKM::IsMine(const CScript& script) const
     case IsMineResult::NO:
         return ISMINE_NO;
     case IsMineResult::WATCH_ONLY:
-        return ISMINE_WATCH_ONLY;
     case IsMineResult::SPENDABLE:
         return ISMINE_SPENDABLE;
     }

src/wallet/types.h

@@ -25,7 +25,6 @@ namespace wallet {
  *
  * For LegacyScriptPubKeyMan,
  * ISMINE_NO: the scriptPubKey is not in the wallet;
- * ISMINE_WATCH_ONLY: the scriptPubKey has been imported into the wallet;
  * ISMINE_SPENDABLE: the scriptPubKey corresponds to an address owned by the wallet user (can spend with the private key);
  * ISMINE_USED: the scriptPubKey corresponds to a used address owned by the wallet user;
  * ISMINE_ALL: all ISMINE flags except for USED;
@@ -40,10 +39,9 @@ namespace wallet {
  */
 enum isminetype : unsigned int {
     ISMINE_NO         = 0,
-    ISMINE_WATCH_ONLY = 1 << 0,
     ISMINE_SPENDABLE  = 1 << 1,
     ISMINE_USED       = 1 << 2,
-    ISMINE_ALL        = ISMINE_WATCH_ONLY | ISMINE_SPENDABLE,
+    ISMINE_ALL        = ISMINE_SPENDABLE,
     ISMINE_ALL_USED   = ISMINE_ALL | ISMINE_USED,
     ISMINE_ENUM_ELEMENTS,
 };