[llvm-readobj/llvm-readelf] Delete --arm-attributes (alias for --arch-specific)

D68110 added --arch-specific (supported by GNU readelf) and made
--arm-attributes an alias for it. The tests were later migrated to use
--arch-specific.

Note, llvm-readelf --arch-specific currently just uses llvm-readobj
style output for ARM attributes. The readelf-style output is not
implemented.

Reviewed By: compnerd, kongyi, rupprecht

Differential Revision: https://reviews.llvm.org/D68196

llvm-svn: 373291
diff --git a/llvm/docs/CommandGuide/llvm-readelf.rst b/llvm/docs/CommandGuide/llvm-readelf.rst
index efb3f6a..2868d0b 100644
--- a/llvm/docs/CommandGuide/llvm-readelf.rst
+++ b/llvm/docs/CommandGuide/llvm-readelf.rst
@@ -28,9 +28,9 @@
 
  Display the address-significance table.
 
-.. option:: --arm-attributes
+.. option:: --arch-specific, -A
 
- Display the ARM attributes section. Only applicable for ARM architectures.
+ Display architecture-specific information, e.g. the ARM attributes section on ARM.
 
 .. option:: --color