Postpone introducing common StringBuilder.capacity() function

Its support complicates JS StringBuilder implementation with no actual
performance improvements. Benefits of having capacity() function
in common code are also not completely clear.

Relates to KT-33069
#KT-40168

libraries/stdlib/test/text/StringBuilderTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -236,8 +236,9 @@ class StringBuilderTest {
     }
 
     @Test
+    @Suppress("DEPRECATION_ERROR")
     fun capacityTest() {
-        assertEquals(100, StringBuilder(100).capacity())
+//        assertEquals(100, StringBuilder(100).capacity()) // not implemented in JS
 
         StringBuilder("string builder from string capacity test").let { sb ->
             assertTrue(sb.capacity() >= sb.length)
@@ -251,7 +252,7 @@ class StringBuilderTest {
             sb.ensureCapacity(1)
             assertTrue(sb.capacity() >= sb.length)
             sb.ensureCapacity(sb.length * 10)
-            assertTrue(sb.capacity() >= sb.length * 10)
+//            assertTrue(sb.capacity() >= sb.length * 10) // not implemented in JS
         }
     }
 
@@ -423,11 +424,11 @@ class StringBuilderTest {
     fun trimToSize() {
         StringBuilder("my trimToSize test").let { sb ->
             assertEquals(18, sb.length)
-            assertTrue(sb.capacity() >= sb.length)
+//            assertTrue(sb.capacity() >= sb.length)
             sb.append('1')
             sb.trimToSize()
             assertEquals(19, sb.length)
-            assertTrue(sb.capacity() >= sb.length)
+//            assertTrue(sb.capacity() >= sb.length)
         }
     }