Use skylark-preferred quote char for string literal

We currently have no need to discern between strings quoted with ' or ". While it could be
nice for something one day (and may have been in the past), it's yagni now. Removing the
distinction simplifies string concatenation.

--
PiperOrigin-RevId: 148273400
MOS_MIGRATED_REVID=148273400
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
index e499907..fd97117 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
@@ -606,9 +606,8 @@
   private StringLiteral parseStringLiteral() {
     Preconditions.checkState(token.kind == TokenKind.STRING);
     int end = token.right;
-    char quoteChar = lexer.charAt(token.left);
     StringLiteral literal =
-        setLocation(new StringLiteral((String) token.value, quoteChar), token.left, end);
+        setLocation(new StringLiteral((String) token.value), token.left, end);
 
     nextToken();
     if (token.kind == TokenKind.STRING) {
@@ -957,9 +956,7 @@
       if (expr instanceof StringLiteral && secondary instanceof StringLiteral) {
         StringLiteral left = (StringLiteral) expr;
         StringLiteral right = (StringLiteral) secondary;
-        if (left.getQuoteChar() == right.getQuoteChar()) {
-          return new StringLiteral(left.getValue() + right.getValue(), left.getQuoteChar());
-        }
+        return new StringLiteral(left.getValue() + right.getValue());
       }
     }
     return new BinaryOperatorExpression(operator, expr, secondary);