Revert "transition matrix44 to opt-in only"

This reverts commit 0f1f87d.

Reason for revert: google3 and flutter also need the guard

Original change's description:
> transition matrix44 to opt-in only
> 
> In service of https://chromium-review.googlesource.com/c/chromium/src/+/2067862/
> 
> Change-Id: Ib6fd24c16c295fb4211dc295268af1e6f7f3fc45
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/283661
> Reviewed-by: Florin Malita <fmalita@chromium.org>
> Commit-Queue: Mike Reed <reed@google.com>

TBR=fmalita@chromium.org,reed@google.com

Change-Id: I7c8cf2bc67aa267d442d0ca663e8378aa8feb409
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/283896
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>

Author: reed-at-google

gn/tests.gni

@@ -142,7 +142,6 @@ tests_sources = [
   "$_tests/LRUCacheTest.cpp",
   "$_tests/LayerDrawLooperTest.cpp",
   "$_tests/LazyProxyTest.cpp",
-  "$_tests/M44Test.cpp",
   "$_tests/MD5Test.cpp",
   "$_tests/MallocPixelRefTest.cpp",
   "$_tests/MaskCacheTest.cpp",

include/core/SkMatrix44.h

@@ -11,8 +11,6 @@
 #include "include/core/SkMatrix.h"
 #include "include/core/SkScalar.h"
 
-#ifdef SK_SUPPORT_LEGACY_MATRIX44
-
 #include <atomic>
 #include <cstring>
 
@@ -392,4 +390,3 @@ class SK_API SkMatrix44 {
 };
 
 #endif
-#endif

src/core/SkMatrix44.cpp

@@ -9,8 +9,6 @@
 #include <type_traits>
 #include <utility>
 
-#ifdef SK_SUPPORT_LEGACY_MATRIX44
-
 // Copying SkMatrix44 byte-wise is performance-critical to Blink. This class is
 // contained in several Transform classes, which are copied multiple times
 // during the rendering life cycle. See crbug.com/938563 for reference.
@@ -999,5 +997,3 @@ SkMatrix44::operator SkMatrix() const {
 
     return dst;
 }
-
-#endif