Drop the C shim for float formatting now that jsonpull is C++

json_print_one() reached fpfmt through dtoa_shortest(), a C-linkage
wrapper in text.cpp that strdup()ed the formatted string so the C
jsonpull could take it and free() it. jsonpull has been C++ since 4f26211,
so it can append the std::string directly and skip the copy, the
allocation, and the free.

That was the shim's only caller, so fpfmt/fpfmt.h goes away with it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014wJRAuhMninQE4wK2TUfuZ

text.cpp

@@ -6,7 +6,6 @@
 #include <vector>
 #include "text.hpp"
 #include "fpfmt/fpfmt.hpp"
-#include "fpfmt/fpfmt.h"
 #include "errors.hpp"
 
 /**
@@ -176,17 +175,6 @@ std::string format_commandline(int argc, char **argv) {
 	return out;
 }
 
-// for jsonpull to call from C
-char *dtoa_shortest(double val) {
-	std::string s = fpfmt::dtoa(val);
-	char *dup = strdup(s.c_str());
-	if (dup == NULL) {
-		perror("strdup");
-		exit(EXIT_MEMORY);
-	}
-	return dup;
-}
-
 // to work with data from https://github.com/kmike/text-unidecode
 std::vector<std::string> read_unidecode(const char *fname) {
 	std::string data;