[gdb/cli] Fix help text of maint set ignore-prologue-end-flag
I noticed here:
...
(gdb) help maint set ignore-prologue-end-flag
Set if the PROLOGUE-END flag is ignored.
The PROLOGUE-END flag from the line-table entries is used to place \
breakpoints past the prologue of functions. Disabeling its use use forces \
the use of prologue scanners.
...
a typo in "Disabeling" and accidental word repetition "use use".