Merge LabelImport class and SkylarkImport; delete SkylarkImports

After the simplifications in unknown commit and https://github.com/bazelbuild/bazel/commit/024b4951b4b0a89f5a1dd5f2a4fbfd4297d47e58, we're now able to delete SkylarkImports.
We went from one interface, one abstract class and two other classes, to just one class.

RELNOTES: None.
PiperOrigin-RevId: 243654192
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
index 3e521aa..bc1dff2 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
@@ -73,8 +73,7 @@
 import com.google.devtools.build.lib.skyframe.SkyframeExecutor;
 import com.google.devtools.build.lib.skyframe.TargetPatternPhaseValue;
 import com.google.devtools.build.lib.syntax.SkylarkImport;
-import com.google.devtools.build.lib.syntax.SkylarkImports;
-import com.google.devtools.build.lib.syntax.SkylarkImports.SkylarkImportSyntaxException;
+import com.google.devtools.build.lib.syntax.SkylarkImport.SkylarkImportSyntaxException;
 import com.google.devtools.build.lib.util.Pair;
 import com.google.devtools.build.lib.util.RegexFilter;
 import com.google.devtools.build.skyframe.SkyKey;
@@ -316,7 +315,7 @@
         SkylarkImport skylarkImport;
         try {
           skylarkImport =
-              SkylarkImports.create(
+              SkylarkImport.create(
                   bzlFileLoadLikeString, /* repositoryMapping= */ ImmutableMap.of());
         } catch (SkylarkImportSyntaxException e) {
           throw new ViewCreationFailedException(