[optional.monadic] Remove stray angle brackets on concept name (#7817)

Author: jwakely

source/utilities.tex

@@ -4378,7 +4378,7 @@
 \begin{itemdescr}
 \pnum
 \constraints
-\tcode{F} models \tcode{\libconcept{invocable}<>} and
+\tcode{F} models \libconcept{invocable} and
 \tcode{T} models \libconcept{copy_constructible}.
 
 \pnum
@@ -4405,7 +4405,7 @@
 \begin{itemdescr}
 \pnum
 \constraints
-\tcode{F} models \tcode{\libconcept{invocable}<>} and
+\tcode{F} models \libconcept{invocable} and
 \tcode{T} models \libconcept{move_constructible}.
 
 \pnum