Don't return a const std::string from GetData

It has zero benefit and forces an extra copy.

aegisub/src/ass_attachment.h

@@ -46,7 +46,7 @@ public:
 	/// @param raw If false, remove the SSA filename mangling
 	std::string GetFileName(bool raw=false) const;
 
-	const std::string GetEntryData() const override { return entry_data;  }
+	std::string GetEntryData() const override { return entry_data;  }
 	AssEntryGroup Group() const override { return group; }
 	AssAttachment *Clone() const override { return new AssAttachment(*this); }
 

aegisub/src/ass_dialogue.h

@@ -170,7 +170,7 @@ public:
 
 	/// Update the text of the line from parsed blocks
 	void UpdateText(boost::ptr_vector<AssDialogueBlock>& blocks);
-	const std::string GetEntryData() const override { return GetData(false); }
+	std::string GetEntryData() const override { return GetData(false); }
 
 	/// Get the line as SSA rather than ASS
 	std::string GetSSAText() const override { return GetData(true); }

aegisub/src/ass_entry.h

@@ -60,7 +60,7 @@ public:
 	std::string const& GroupHeader(bool ssa=false) const;
 
 	/// @brief Get this line's raw entry data in ASS format
-	virtual const std::string GetEntryData() const=0;
+	virtual std::string GetEntryData() const=0;
 
 	/// Get this line in SSA format
 	virtual std::string GetSSAText() const { return GetEntryData(); }

aegisub/src/ass_info.h

@@ -28,7 +28,7 @@ public:
 
 	AssInfo *Clone() const override { return new AssInfo(*this); }
 	AssEntryGroup Group() const override { return AssEntryGroup::INFO; }
-	const std::string GetEntryData() const override { return key + ": " + value; }
+	std::string GetEntryData() const override { return key + ": " + value; }
 	std::string GetSSAText() const override { return boost::iequals(key, "scripttype: v4.00+") ? "ScriptType: v4.00" : GetEntryData(); }
 
 	std::string Key() const { return key; }

aegisub/src/ass_style.h

@@ -77,7 +77,7 @@ public:
 	AssStyle();
 	AssStyle(std::string const& data, int version=1);
 
-	const std::string GetEntryData() const override { return data; }
+	std::string GetEntryData() const override { return data; }
 	std::string GetSSAText() const override;
 	AssEntryGroup Group() const override { return AssEntryGroup::STYLE; }
 	AssStyle *Clone() const override { return new AssStyle(*this); }