Fix/suppress tools google-explicit-constructor warnings

* Add explicit to conversion constructors/operators
* Remove redundant explicit of copy constructors

Bug: 28341362
Test: make with WITH_TIDY=1 DEFAULT_GLOBAL_TIDY_CHECKS=-*,google-explicit-constructor
Change-Id: Ic11c22c59beb7aa32b878a23315b1036ca4e3c6a
diff --git a/tools/bit/command.h b/tools/bit/command.h
index fb44900..dd7103e 100644
--- a/tools/bit/command.h
+++ b/tools/bit/command.h
@@ -25,7 +25,7 @@
 
 struct Command
 {
-    Command(const string& prog);
+    explicit Command(const string& prog);
     ~Command();
 
     void AddArg(const string& arg);
diff --git a/tools/streaming_proto/Errors.h b/tools/streaming_proto/Errors.h
index f14bbfd..bddd981 100644
--- a/tools/streaming_proto/Errors.h
+++ b/tools/streaming_proto/Errors.h
@@ -11,7 +11,7 @@
 struct Error
 {
     Error();
-    explicit Error(const Error& that);
+    Error(const Error& that);
     Error(const string& filename, int lineno, const char* message);
 
     string filename;