backport of 11074 - doc: replace newlines in deprecation with space

[thefourtheye]

Backport of #11074

As it is, each line in the deprecation heading which are wrapped at 80
characters in the *.md files, are shown in different lines. For example

> Stability: 0 - Deprecated: Use
> `Buffer.from(arrayBuffer[, byteOffset [, length]])`
> instead.

is shown in three different lines. This patch replaces the newlines
with space characters, so that the output will be in single line.

PR-URL: #11074

Reviewed-By: Anna Henningsen [email protected]
Reviewed-By: Jeremiah Senkpiel [email protected]
Reviewed-By: Colin Ihrig [email protected]
Reviewed-By: Timothy Gu [email protected]
Reviewed-By: James M Snell [email protected]
Reviewed-By: Luigi Pinca [email protected]
Reviewed-By: Michaël Zasso [email protected]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

[MylesBorins]

@thefourtheye this was already cherry-picked in f62b879