buf: remove internal git_buf_text namespace

The `git_buf_text` namespace is unnecessary and strange.  Remove it,
just keep the functions prefixed with `git_buf`.

Author: ethomson

src/attr_file.c

@@ -10,7 +10,6 @@
 #include "repository.h"
 #include "filebuf.h"
 #include "attrcache.h"
-#include "buf_text.h"
 #include "git2/blob.h"
 #include "git2/tree.h"
 #include "blob.h"
@@ -192,7 +191,7 @@ int git_attr_file__load(
 
 	/* advance over a UTF8 BOM */
 	content_str = git_buf_cstr(&content);
-	bom_offset = git_buf_text_detect_bom(&bom, &content);
+	bom_offset = git_buf_detect_bom(&bom, &content);
 
 	if (bom == GIT_BOM_UTF8)
 		content_str += bom_offset;

src/blob.c

@@ -14,7 +14,6 @@
 
 #include "filebuf.h"
 #include "filter.h"
-#include "buf_text.h"
 
 const void *git_blob_rawcontent(const git_blob *blob)
 {
@@ -401,7 +400,7 @@ int git_blob_is_binary(const git_blob *blob)
 
 	git_buf_attach_notowned(&content, git_blob_rawcontent(blob),
 		(size_t)min(size, GIT_FILTER_BYTES_TO_CHECK_NUL));
-	return git_buf_text_is_binary(&content);
+	return git_buf_is_binary(&content);
 }
 
 int git_blob_filter_options_init(