Fix incorrect delete function call in TextureTest

The test must call glDeleteBuffers to delete a buffer instead of
glDeleteTextures. This was one reason behind the texture tests failing
on the GL backend.

BUG=angleproject:1261
TEST=angle_end2end_tests

Change-Id: I67042f6948146f3c3fca9e01231b0c4935a6f08d
Reviewed-on: https://chromium-review.googlesource.com/321611
Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/tests/gl_tests/TextureTest.cpp b/src/tests/gl_tests/TextureTest.cpp
index 821fb7e..09fa0c8 100644
--- a/src/tests/gl_tests/TextureTest.cpp
+++ b/src/tests/gl_tests/TextureTest.cpp
@@ -811,7 +811,7 @@
         glUniform1i(mTexture2DUniformLocation, 0);
         drawQuad(mProgram, "position", 0.5f);
         glDeleteTextures(1, &tex2D);
-        glDeleteTextures(1, &pbo);
+        glDeleteBuffers(1, &pbo);
         EXPECT_GL_NO_ERROR();
         EXPECT_PIXEL_EQ(3 * width / 4, 3 * height / 4, 0, 0, 0, 255);
         EXPECT_PIXEL_EQ(width / 4, height / 4, 255, 0, 0, 255);