Strict single-letter extensions on Table 28.1 (Standard ISA extension…

… names) (#838)

* Remove "B", "K" and "J" from standard names

They are not going to be single-letter extension names.

Because "Z*" extensions are first ordered with the second character by
extension category list "IMAFDQLCBKJTPV", those single-letters are not
necessary in the table (they can be even misleading and harmful).

* Make "V" extension singular in the naming table

"Zv*" are vector subextensions but "V" is now a single extension.
So, "V" must be singular in the standard ISA extension names table.

src/naming.tex

@@ -165,11 +165,8 @@ \section{Subset Naming Convention}
 \hline
 Quad-Precision Floating-Point & Q & D\\
 16-bit Compressed Instructions & C & \\
-Bit Manipulation & B & \\
-Cryptography Extensions & K & \\
-Dynamic Languages & J & \\
 Packed-SIMD Extensions & P & \\
-Vector Extensions & V & \\
+Vector Extension & V & \\
 Control and Status Register Access & Zicsr & \\
 Instruction-Fetch Fence & Zifencei & \\
 Misaligned Atomics & Zam & A \\