Rename all testdata loading files to conform to a single naming scheme

The scheme is:
- loadBytes: returns a ByteSource of the data
- loadFile: returns a string using UTF8 encoding, optionally applying
  substitutions

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177606406

javatests/google/registry/tmch/TmchTestData.java

@@ -32,13 +32,13 @@ public final class TmchTestData {
   }
 
   /** Loads data from file in {@code tmch/testdata/} as a String. */
-  public static String loadString(String filename) {
+  public static String loadFile(String filename) {
     return TestDataHelper.loadFile(TmchTestData.class, filename);
   }
 
   /** Extracts SMD XML from an ASCII-armored file. */
   public static byte[] loadSmd(String file) {
-    String data = loadString(file);
+    String data = loadFile(file);
     return base64().decode(whitespace().removeFrom(data.substring(
         data.indexOf(BEGIN_ENCODED_SMD) + BEGIN_ENCODED_SMD.length(),
         data.indexOf(END_ENCODED_SMD))));