llvm 13 is now not supported (#1612)

Author: tshepang

src/llvm-coverage-instrumentation.md

@@ -223,9 +223,7 @@ details of the [_LLVM Coverage Mapping Format_][coverage-mapping-format]
 (Version 6).[^llvm-and-covmap-versions]
 
 [^llvm-and-covmap-versions]:
-The Rust compiler (as of <!-- date-check: --> Jan 2023) supports _LLVM Coverage Mapping Format_ 6.
-It was introduced in _LLVM 13_, which is, as of <!-- date-check: Jan 2023 --> this writing,
-the minimum supported LLVM version.
+The Rust compiler (as of <!-- date-check: --> Feb 2023) supports _LLVM Coverage Mapping Format_ 6.
 The Rust compiler will automatically use the most up-to-date coverage mapping format
 version that is compatible with the compiler's built-in version of LLVM.