Remove imports of anyhow::Error and use named path anyhow::Error in place.

This is done for the same reason as for anyhow::Result and
core::result::Result types.

Error is whidely used name and IMO it usually good to keep it standard.
Apart from that I think assosicated type specification looks fore
readable when anyhow::Error is used in place. For example:

    type Error = Error;

was replaced with

    type Error = anyhow::Error;

Changes:
- Replace usage of imported unquolified Error type with anyhow::Error.
- Remove imports of anyhow::Error.

database/src/types.rs

@@ -2,7 +2,7 @@ use std::convert::TryFrom;
 use std::fmt;
 use std::str::FromStr;
 
-use anyhow::{Error, anyhow};
+use anyhow::anyhow;
 use hex::ToHex;
 use r2d2_sqlite::rusqlite::types::FromSql;
 use r2d2_sqlite::rusqlite::types::FromSqlError;
@@ -47,7 +47,7 @@ impl ToSql for Email {
 }
 
 impl TryFrom<&UserID> for Email {
-    type Error = Error;
+    type Error = anyhow::Error;
 
     fn try_from(uid: &UserID) -> anyhow::Result<Self> {
         if let Some(address) = uid.email2()? {
@@ -90,7 +90,7 @@ impl fmt::Display for Email {
 }
 
 impl FromStr for Email {
-    type Err = Error;
+    type Err = anyhow::Error;
 
     fn from_str(s: &str) -> anyhow::Result<Email> {
         Email::try_from(&UserID::from(s))
@@ -117,7 +117,7 @@ impl ToSql for Fingerprint {
 }
 
 impl TryFrom<sequoia_openpgp::Fingerprint> for Fingerprint {
-    type Error = Error;
+    type Error = anyhow::Error;
 
     fn try_from(fpr: sequoia_openpgp::Fingerprint) -> anyhow::Result<Self> {
         match fpr {
@@ -156,7 +156,7 @@ impl<'de> Deserialize<'de> for Fingerprint {
 }
 
 impl FromStr for Fingerprint {
-    type Err = Error;
+    type Err = anyhow::Error;
 
     fn from_str(s: &str) -> anyhow::Result<Fingerprint> {
         match sequoia_openpgp::Fingerprint::from_hex(s)? {
@@ -189,7 +189,7 @@ impl ToSql for KeyID {
 }
 
 impl TryFrom<sequoia_openpgp::Fingerprint> for KeyID {
-    type Error = Error;
+    type Error = anyhow::Error;
 
     fn try_from(fpr: sequoia_openpgp::Fingerprint) -> anyhow::Result<Self> {
         match fpr {
@@ -225,7 +225,7 @@ impl fmt::Display for KeyID {
 }
 
 impl FromStr for KeyID {
-    type Err = Error;
+    type Err = anyhow::Error;
 
     fn from_str(s: &str) -> anyhow::Result<KeyID> {
         match sequoia_openpgp::KeyID::from_hex(s)? {