[turbofan] Remove STYLE file

What it says is can be summarized as "follow the style guide" plus some
notes about TODOs that don't reflect reality.

Change-Id: I058a2d11a505c4f9a57f518daa142cc1240109d5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1649354Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62245}

src/compiler/STYLE

-Compiler Coding Style
-=====================
-
-Coding style for the TurboFan compiler generally follows the Google C++ Style
-Guide and the Chromium Coding Style. The notes below are usually just extensions
-beyond what the Google style guide already says. If this document doesn't
-mention a rule, follow the Google C++ style.
-
-
-TODOs
------
-We use the following convention for putting TODOs into the code:
-
-  * A TODO(turbofan) implies a performance improvement opportunity.
-  * A TODO(name) implies an incomplete implementation.
-
-
-Use of C++11 auto keyword
--------------------------
-Use auto to avoid type names that are just clutter. Continue to use manifest
-type declarations when it helps readability, and never use auto for anything
-but local variables, in particular auto should only be used where it is obvious
-from context what the type is:
-
-  for (auto block : x->blocks())  // clearly a Block of some kind
-  for (auto instr : x->instructions())  // clearly an Instruction of some kind
-
-  for (auto b : x->predecessors()) // less clear, better to make it explicit
-  for (BasicBlock* b : x->predecessors()) // now clear