Remove unnecessary and inconsistent "final" from color sinks (#3430)

The use of "final" differed between ansicolor_sink and wincolor_sink,
resulting in the code inheriting from std{err,out}_color_sink classes,
which are defined as one or the other on different platforms, being able
to override most of the functions under non-Windows platforms, but not
under Windows.

This seems gratuitously inconsistent, so just remove all "final"
keywords from both classes, especially because there doesn't seem any
good reason to use it and the other sink classes don't use it (with the
exception of base_sink, which is special).

This also incidentally fixes using "final override" in most places but
"override final" in wincolor_sink.h.

Fixes #3429.

include/spdlog/sinks/ansicolor_sink.h

@@ -40,7 +40,7 @@ public:
 
     void log(const details::log_msg &msg) override;
     void flush() override;
-    void set_pattern(const std::string &pattern) final override;
+    void set_pattern(const std::string &pattern) override;
     void set_formatter(std::unique_ptr<spdlog::formatter> sink_formatter) override;
 
     // Formatting codes

include/spdlog/sinks/wincolor_sink.h

@@ -31,10 +31,10 @@ public:
 
     // change the color for the given level
     void set_color(level::level_enum level, std::uint16_t color);
-    void log(const details::log_msg &msg) final override;
+    void log(const details::log_msg &msg) override;
-    void flush() final override;
+    void flush() override;
-    void set_pattern(const std::string &pattern) override final;
+    void set_pattern(const std::string &pattern) override;
-    void set_formatter(std::unique_ptr<spdlog::formatter> sink_formatter) override final;
+    void set_formatter(std::unique_ptr<spdlog::formatter> sink_formatter) override;
     void set_color_mode(color_mode mode);
 
 protected: